doc/src/sgml/catalogs.sgml

   1 <!-- $PostgreSQL$ -->
   2 <!--
   3  Documentation of the system catalogs, directed toward PostgreSQL developers
   4  -->
   5
   6 <chapter id="catalogs">
   7  <title>System Catalogs</title>
   8
   9   <para>
  10    The system catalogs are the place where a relational database
  11    management system stores schema metadata, such as information about
  12    tables and columns, and internal bookkeeping information.
  13    <productname>PostgreSQL</productname>'s system catalogs are regular
  14    tables.  You can drop and recreate the tables, add columns, insert
  15    and update values, and severely mess up your system that way.
  16    Normally, one should not change the system catalogs by hand, there
  17    are always SQL commands to do that.  (For example, <command>CREATE
  18    DATABASE</command> inserts a row into the
  19    <structname>pg_database</structname> catalog &mdash; and actually
  20    creates the database on disk.)  There are some exceptions for
  21    particularly esoteric operations, such as adding index access methods.
  22   </para>
  23
  24  <sect1 id="catalogs-overview">
  25   <title>Overview</title>
  26
  27   <para>
  28    <xref linkend="catalog-table"> lists the system catalogs.
  29    More detailed documentation of each catalog follows below.
  30   </para>
  31
  32   <para>
  33    Most system catalogs are copied from the template database during
  34    database creation and are thereafter database-specific. A few
  35    catalogs are physically shared across all databases in a cluster;
  36    these are noted in the descriptions of the individual catalogs.
  37   </para>
  38
  39   <table id="catalog-table">
  40    <title>System Catalogs</title>
  41
  42    <tgroup cols="2">
  43     <thead>
  44      <row>
  45       <entry>Catalog Name</entry>
  46       <entry>Purpose</entry>
  47      </row>
  48     </thead>
  49
  50     <tbody>
  51      <row>
  52       <entry><link linkend="catalog-pg-aggregate"><structname>pg_aggregate</structname></link></entry>
  53       <entry>aggregate functions</entry>
  54      </row>
  55
  56      <row>
  57       <entry><link linkend="catalog-pg-am"><structname>pg_am</structname></link></entry>
  58       <entry>index access methods</entry>
  59      </row>
  60
  61      <row>
  62       <entry><link linkend="catalog-pg-amop"><structname>pg_amop</structname></link></entry>
  63       <entry>access method operators</entry>
  64      </row>
  65
  66      <row>
  67       <entry><link linkend="catalog-pg-amproc"><structname>pg_amproc</structname></link></entry>
  68       <entry>access method support procedures</entry>
  69      </row>
  70
  71      <row>
  72       <entry><link linkend="catalog-pg-attrdef"><structname>pg_attrdef</structname></link></entry>
  73       <entry>column default values</entry>
  74      </row>
  75
  76      <row>
  77       <entry><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link></entry>
  78       <entry>table columns (<quote>attributes</quote>)</entry>
  79      </row>
  80
  81      <row>
  82       <entry><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link></entry>
  83       <entry>authorization identifiers (roles)</entry>
  84      </row>
  85
  86      <row>
  87       <entry><link linkend="catalog-pg-auth-members"><structname>pg_auth_members</structname></link></entry>
  88       <entry>authorization identifier membership relationships</entry>
  89      </row>
  90
  91      <row>
  92       <entry><link linkend="catalog-pg-autovacuum"><structname>pg_autovacuum</structname></link></entry>
  93       <entry>per-relation autovacuum configuration parameters</entry>
  94      </row>
  95
  96      <row>
  97       <entry><link linkend="catalog-pg-cast"><structname>pg_cast</structname></link></entry>
  98       <entry>casts (data type conversions)</entry>
  99      </row>
 100
 101      <row>
 102       <entry><link linkend="catalog-pg-class"><structname>pg_class</structname></link></entry>
 103       <entry>tables, indexes, sequences, views (<quote>relations</quote>)</entry>
 104      </row>
 105
 106      <row>
 107       <entry><link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link></entry>
 108       <entry>check constraints, unique constraints, primary key constraints, foreign key constraints</entry>
 109      </row>
 110
 111      <row>
 112       <entry><link linkend="catalog-pg-conversion"><structname>pg_conversion</structname></link></entry>
 113       <entry>encoding conversion information</entry>
 114      </row>
 115
 116      <row>
 117       <entry><link linkend="catalog-pg-database"><structname>pg_database</structname></link></entry>
 118       <entry>databases within this database cluster</entry>
 119      </row>
 120
 121      <row>
 122       <entry><link linkend="catalog-pg-depend"><structname>pg_depend</structname></link></entry>
 123       <entry>dependencies between database objects</entry>
 124      </row>
 125
 126      <row>
 127       <entry><link linkend="catalog-pg-description"><structname>pg_description</structname></link></entry>
 128       <entry>descriptions or comments on database objects</entry>
 129      </row>
 130
 131      <row>
 132       <entry><link linkend="catalog-pg-enum"><structname>pg_enum</structname></link></entry>
 133       <entry>enum label and value definitions</entry>
 134      </row>
 135
 136      <row>
 137       <entry><link linkend="catalog-pg-foreign-data-wrapper"><structname>pg_foreign_data_wrapper</structname></link></entry>
 138       <entry>foreign-data wrapper definitions</entry>
 139      </row>
 140
 141      <row>
 142       <entry><link linkend="catalog-pg-foreign-server"><structname>pg_foreign_server</structname></link></entry>
 143       <entry>foreign server definitions</entry>
 144      </row>
 145
 146      <row>
 147       <entry><link linkend="catalog-pg-index"><structname>pg_index</structname></link></entry>
 148       <entry>additional index information</entry>
 149      </row>
 150
 151      <row>
 152       <entry><link linkend="catalog-pg-inherits"><structname>pg_inherits</structname></link></entry>
 153       <entry>table inheritance hierarchy</entry>
 154      </row>
 155
 156      <row>
 157       <entry><link linkend="catalog-pg-language"><structname>pg_language</structname></link></entry>
 158       <entry>languages for writing functions</entry>
 159      </row>
 160
 161      <row>
 162       <entry><link linkend="catalog-pg-largeobject"><structname>pg_largeobject</structname></link></entry>
 163       <entry>large objects</entry>
 164      </row>
 165
 166      <row>
 167       <entry><link linkend="catalog-pg-listener"><structname>pg_listener</structname></link></entry>
 168       <entry>asynchronous notification support</entry>
 169      </row>
 170
 171      <row>
 172       <entry><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link></entry>
 173       <entry>schemas</entry>
 174      </row>
 175
 176      <row>
 177       <entry><link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link></entry>
 178       <entry>access method operator classes</entry>
 179      </row>
 180
 181      <row>
 182       <entry><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link></entry>
 183       <entry>operators</entry>
 184      </row>
 185
 186      <row>
 187       <entry><link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link></entry>
 188       <entry>access method operator families</entry>
 189      </row>
 190
 191      <row>
 192       <entry><link linkend="catalog-pg-pltemplate"><structname>pg_pltemplate</structname></link></entry>
 193       <entry>template data for procedural languages</entry>
 194      </row>
 195
 196      <row>
 197       <entry><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link></entry>
 198       <entry>functions and procedures</entry>
 199      </row>
 200
 201      <row>
 202       <entry><link linkend="catalog-pg-rewrite"><structname>pg_rewrite</structname></link></entry>
 203       <entry>query rewrite rules</entry>
 204      </row>
 205
 206      <row>
 207       <entry><link linkend="catalog-pg-shdepend"><structname>pg_shdepend</structname></link></entry>
 208       <entry>dependencies on shared objects</entry>
 209      </row>
 210
 211      <row>
 212       <entry><link linkend="catalog-pg-shdescription"><structname>pg_shdescription</structname></link></entry>
 213       <entry>comments on shared objects</entry>
 214      </row>
 215
 216      <row>
 217       <entry><link linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link></entry>
 218       <entry>planner statistics</entry>
 219      </row>
 220
 221      <row>
 222       <entry><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link></entry>
 223       <entry>tablespaces within this database cluster</entry>
 224      </row>
 225
 226      <row>
 227       <entry><link linkend="catalog-pg-trigger"><structname>pg_trigger</structname></link></entry>
 228       <entry>triggers</entry>
 229      </row>
 230
 231      <row>
 232       <entry><link linkend="catalog-pg-ts-config"><structname>pg_ts_config</structname></link></entry>
 233       <entry>text search configurations</entry>
 234      </row>
 235
 236      <row>
 237       <entry><link linkend="catalog-pg-ts-config-map"><structname>pg_ts_config_map</structname></link></entry>
 238       <entry>text search configurations' token mappings</entry>
 239      </row>
 240
 241      <row>
 242       <entry><link linkend="catalog-pg-ts-dict"><structname>pg_ts_dict</structname></link></entry>
 243       <entry>text search dictionaries</entry>
 244      </row>
 245
 246      <row>
 247       <entry><link linkend="catalog-pg-ts-parser"><structname>pg_ts_parser</structname></link></entry>
 248       <entry>text search parsers</entry>
 249      </row>
 250
 251      <row>
 252       <entry><link linkend="catalog-pg-ts-template"><structname>pg_ts_template</structname></link></entry>
 253       <entry>text search templates</entry>
 254      </row>
 255
 256      <row>
 257       <entry><link linkend="catalog-pg-type"><structname>pg_type</structname></link></entry>
 258       <entry>data types</entry>
 259      </row>
 260
 261      <row>
 262       <entry><link linkend="catalog-pg-user-mapping"><structname>pg_user_mapping</structname></link></entry>
 263       <entry>mappings of users to foreign servers</entry>
 264      </row>
 265     </tbody>
 266    </tgroup>
 267   </table>
 268  </sect1>
 269
 270
 271  <sect1 id="catalog-pg-aggregate">
 272   <title><structname>pg_aggregate</structname></title>
 273
 274   <indexterm zone="catalog-pg-aggregate">
 275    <primary>pg_aggregate</primary>
 276   </indexterm>
 277
 278   <para>
 279    The catalog <structname>pg_aggregate</structname> stores information about
 280    aggregate functions.  An aggregate function is a function that
 281    operates on a set of values (typically one column from each row
 282    that matches a query condition) and returns a single value computed
 283    from all these values.  Typical aggregate functions are
 284    <function>sum</function>, <function>count</function>, and
 285    <function>max</function>.  Each entry in
 286    <structname>pg_aggregate</structname> is an extension of an entry
 287    in <structname>pg_proc</structname>.  The <structname>pg_proc</structname>
 288    entry carries the aggregate's name, input and output data types, and
 289    other information that is similar to ordinary functions.
 290   </para>
 291
 292   <table>
 293    <title><structname>pg_aggregate</> Columns</title>
 294
 295    <tgroup cols=4>
 296     <thead>
 297      <row>
 298       <entry>Name</entry>
 299       <entry>Type</entry>
 300       <entry>References</entry>
 301       <entry>Description</entry>
 302      </row>
 303     </thead>
 304     <tbody>
 305      <row>
 306       <entry><structfield>aggfnoid</structfield></entry>
 307       <entry><type>regproc</type></entry>
 308       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 309       <entry><structname>pg_proc</structname> OID of the aggregate function</entry>
 310      </row>
 311      <row>
 312       <entry><structfield>aggtransfn</structfield></entry>
 313       <entry><type>regproc</type></entry>
 314       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 315       <entry>Transition function</entry>
 316      </row>
 317      <row>
 318       <entry><structfield>aggfinalfn</structfield></entry>
 319       <entry><type>regproc</type></entry>
 320       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 321       <entry>Final function (zero if none)</entry>
 322      </row>
 323      <row>
 324       <entry><structfield>aggsortop</structfield></entry>
 325       <entry><type>oid</type></entry>
 326       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
 327       <entry>Associated sort operator (zero if none)</entry>
 328      </row>
 329      <row>
 330       <entry><structfield>aggtranstype</structfield></entry>
 331       <entry><type>oid</type></entry>
 332       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 333       <entry>Data type of the aggregate function's internal transition (state) data</entry>
 334      </row>
 335      <row>
 336       <entry><structfield>agginitval</structfield></entry>
 337       <entry><type>text</type></entry>
 338       <entry></entry>
 339       <entry>
 340        The initial value of the transition state.  This is a text
 341        field containing the initial value in its external string
 342        representation.  If this field is NULL, the transition state
 343        value starts out NULL
 344       </entry>
 345      </row>
 346     </tbody>
 347    </tgroup>
 348   </table>
 349
 350   <para>
 351    New aggregate functions are registered with the <xref
 352    linkend="sql-createaggregate" endterm="sql-createaggregate-title">
 353    command.  See <xref linkend="xaggr"> for more information about
 354    writing aggregate functions and the meaning of the transition
 355    functions, etc.
 356   </para>
 357
 358  </sect1>
 359
 360
 361  <sect1 id="catalog-pg-am">
 362   <title><structname>pg_am</structname></title>
 363
 364   <indexterm zone="catalog-pg-am">
 365    <primary>pg_am</primary>
 366   </indexterm>
 367
 368   <para>
 369    The catalog <structname>pg_am</structname> stores information about index
 370    access methods.  There is one row for each index access method supported by
 371    the system.  The contents of this catalog are discussed in detail in
 372    <xref linkend="indexam">.
 373   </para>
 374
 375   <table>
 376    <title><structname>pg_am</> Columns</title>
 377
 378    <tgroup cols=4>
 379     <thead>
 380      <row>
 381       <entry>Name</entry>
 382       <entry>Type</entry>
 383       <entry>References</entry>
 384       <entry>Description</entry>
 385      </row>
 386     </thead>
 387     <tbody>
 388
 389      <row>
 390       <entry><structfield>amname</structfield></entry>
 391       <entry><type>name</type></entry>
 392       <entry></entry>
 393       <entry>Name of the access method</entry>
 394      </row>
 395
 396      <row>
 397       <entry><structfield>amstrategies</structfield></entry>
 398       <entry><type>int2</type></entry>
 399       <entry></entry>
 400       <entry>Number of operator strategies for this access method,
 401        or zero if access method does not have a fixed set of operator
 402        strategies</entry>
 403      </row>
 404
 405      <row>
 406       <entry><structfield>amsupport</structfield></entry>
 407       <entry><type>int2</type></entry>
 408       <entry></entry>
 409       <entry>Number of support routines for this access method</entry>
 410      </row>
 411
 412      <row>
 413       <entry><structfield>amcanorder</structfield></entry>
 414       <entry><type>bool</type></entry>
 415       <entry></entry>
 416       <entry>Does the access method support ordered scans?</entry>
 417      </row>
 418
 419      <row>
 420       <entry><structfield>amcanbackward</structfield></entry>
 421       <entry><type>bool</type></entry>
 422       <entry></entry>
 423       <entry>Does the access method support backward scanning?</entry>
 424      </row>
 425
 426      <row>
 427       <entry><structfield>amcanunique</structfield></entry>
 428       <entry><type>bool</type></entry>
 429       <entry></entry>
 430       <entry>Does the access method support unique indexes?</entry>
 431      </row>
 432
 433      <row>
 434       <entry><structfield>amcanmulticol</structfield></entry>
 435       <entry><type>bool</type></entry>
 436       <entry></entry>
 437       <entry>Does the access method support multicolumn indexes?</entry>
 438      </row>
 439
 440      <row>
 441       <entry><structfield>amoptionalkey</structfield></entry>
 442       <entry><type>bool</type></entry>
 443       <entry></entry>
 444       <entry>Does the access method support a scan without any constraint
 445        for the first index column?</entry>
 446      </row>
 447
 448      <row>
 449       <entry><structfield>amindexnulls</structfield></entry>
 450       <entry><type>bool</type></entry>
 451       <entry></entry>
 452       <entry>Does the access method support null index entries?</entry>
 453      </row>
 454
 455      <row>
 456       <entry><structfield>amsearchnulls</structfield></entry>
 457       <entry><type>bool</type></entry>
 458       <entry></entry>
 459       <entry>Does the access method support IS NULL searches?</entry>
 460      </row>
 461
 462      <row>
 463       <entry><structfield>amstorage</structfield></entry>
 464       <entry><type>bool</type></entry>
 465       <entry></entry>
 466       <entry>Can index storage data type differ from column data type?</entry>
 467      </row>
 468
 469      <row>
 470       <entry><structfield>amclusterable</structfield></entry>
 471       <entry><type>bool</type></entry>
 472       <entry></entry>
 473       <entry>Can an index of this type be clustered on?</entry>
 474      </row>
 475
 476      <row>
 477       <entry><structfield>amkeytype</structfield></entry>
 478       <entry><type>oid</type></entry>
 479       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 480       <entry>Type of data stored in index, or zero if not a fixed type</entry>
 481      </row>
 482
 483      <row>
 484       <entry><structfield>aminsert</structfield></entry>
 485       <entry><type>regproc</type></entry>
 486       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 487       <entry><quote>Insert this tuple</quote> function</entry>
 488      </row>
 489
 490      <row>
 491       <entry><structfield>ambeginscan</structfield></entry>
 492       <entry><type>regproc</type></entry>
 493       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 494       <entry><quote>Start new scan</quote> function</entry>
 495      </row>
 496
 497      <row>
 498       <entry><structfield>amgettuple</structfield></entry>
 499       <entry><type>regproc</type></entry>
 500       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 501       <entry><quote>Next valid tuple</quote> function</entry>
 502      </row>
 503
 504      <row>
 505       <entry><structfield>amgetbitmap</structfield></entry>
 506       <entry><type>regproc</type></entry>
 507       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 508       <entry><quote>Fetch all valid tuples</quote> function</entry>
 509      </row>
 510
 511      <row>
 512       <entry><structfield>amrescan</structfield></entry>
 513       <entry><type>regproc</type></entry>
 514       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 515       <entry><quote>Restart this scan</quote> function</entry>
 516      </row>
 517
 518      <row>
 519       <entry><structfield>amendscan</structfield></entry>
 520       <entry><type>regproc</type></entry>
 521       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 522       <entry><quote>End this scan</quote> function</entry>
 523      </row>
 524
 525      <row>
 526       <entry><structfield>ammarkpos</structfield></entry>
 527       <entry><type>regproc</type></entry>
 528       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 529       <entry><quote>Mark current scan position</quote> function</entry>
 530      </row>
 531
 532      <row>
 533       <entry><structfield>amrestrpos</structfield></entry>
 534       <entry><type>regproc</type></entry>
 535       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 536       <entry><quote>Restore marked scan position</quote> function</entry>
 537      </row>
 538
 539      <row>
 540       <entry><structfield>ambuild</structfield></entry>
 541       <entry><type>regproc</type></entry>
 542       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 543       <entry><quote>Build new index</quote> function</entry>
 544      </row>
 545
 546      <row>
 547       <entry><structfield>ambulkdelete</structfield></entry>
 548       <entry><type>regproc</type></entry>
 549       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 550       <entry>Bulk-delete function</entry>
 551      </row>
 552
 553      <row>
 554       <entry><structfield>amvacuumcleanup</structfield></entry>
 555       <entry><type>regproc</type></entry>
 556       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 557       <entry>Post-<command>VACUUM</command> cleanup function</entry>
 558      </row>
 559
 560      <row>
 561       <entry><structfield>amcostestimate</structfield></entry>
 562       <entry><type>regproc</type></entry>
 563       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 564       <entry>Function to estimate cost of an index scan</entry>
 565      </row>
 566
 567      <row>
 568       <entry><structfield>amoptions</structfield></entry>
 569       <entry><type>regproc</type></entry>
 570       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 571       <entry>Function to parse and validate <structfield>reloptions</> for an index</entry>
 572      </row>
 573
 574     </tbody>
 575    </tgroup>
 576   </table>
 577
 578  </sect1>
 579
 580
 581  <sect1 id="catalog-pg-amop">
 582   <title><structname>pg_amop</structname></title>
 583
 584   <indexterm zone="catalog-pg-amop">
 585    <primary>pg_amop</primary>
 586   </indexterm>
 587
 588   <para>
 589    The catalog <structname>pg_amop</structname> stores information about
 590    operators associated with access method operator families.  There is one
 591    row for each operator that is a member of an operator family.  An operator
 592    can appear in more than one family, but cannot appear in more than one
 593    position within a family.
 594   </para>
 595
 596   <table>
 597    <title><structname>pg_amop</> Columns</title>
 598
 599    <tgroup cols=4>
 600     <thead>
 601      <row>
 602       <entry>Name</entry>
 603       <entry>Type</entry>
 604       <entry>References</entry>
 605       <entry>Description</entry>
 606      </row>
 607     </thead>
 608     <tbody>
 609
 610      <row>
 611       <entry><structfield>amopfamily</structfield></entry>
 612       <entry><type>oid</type></entry>
 613       <entry><literal><link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link>.oid</literal></entry>
 614       <entry>The operator family this entry is for</entry>
 615      </row>
 616
 617      <row>
 618       <entry><structfield>amoplefttype</structfield></entry>
 619       <entry><type>oid</type></entry>
 620       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 621       <entry>Left-hand input data type of operator</entry>
 622      </row>
 623
 624      <row>
 625       <entry><structfield>amoprighttype</structfield></entry>
 626       <entry><type>oid</type></entry>
 627       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 628       <entry>Right-hand input data type of operator</entry>
 629      </row>
 630
 631      <row>
 632       <entry><structfield>amopstrategy</structfield></entry>
 633       <entry><type>int2</type></entry>
 634       <entry></entry>
 635       <entry>Operator strategy number</entry>
 636      </row>
 637
 638      <row>
 639       <entry><structfield>amopopr</structfield></entry>
 640       <entry><type>oid</type></entry>
 641       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
 642       <entry>OID of the operator</entry>
 643      </row>
 644
 645      <row>
 646       <entry><structfield>amopmethod</structfield></entry>
 647       <entry><type>oid</type></entry>
 648       <entry><literal><link linkend="catalog-pg-am"><structname>pg_am</structname></link>.oid</literal></entry>
 649       <entry>Index access method operator family is for</entry>
 650      </row>
 651
 652     </tbody>
 653    </tgroup>
 654   </table>
 655
 656   <para>
 657    An entry's <structfield>amopmethod</> must match the
 658    <structname>opfmethod</> of its containing operator family (including
 659    <structfield>amopmethod</> here is an intentional denormalization of the
 660    catalog structure for performance reasons).  Also,
 661    <structfield>amoplefttype</> and <structfield>amoprighttype</> must match
 662    the <structfield>oprleft</> and <structfield>oprright</> fields of the
 663    referenced <structname>pg_operator</> entry.
 664   </para>
 665
 666  </sect1>
 667
 668
 669  <sect1 id="catalog-pg-amproc">
 670   <title><structname>pg_amproc</structname></title>
 671
 672   <indexterm zone="catalog-pg-amproc">
 673    <primary>pg_amproc</primary>
 674   </indexterm>
 675
 676   <para>
 677    The catalog <structname>pg_amproc</structname> stores information about
 678    support procedures associated with access method operator families.  There
 679    is one row for each support procedure belonging to an operator family.
 680   </para>
 681
 682   <table>
 683    <title><structname>pg_amproc</structname> Columns</title>
 684
 685    <tgroup cols=4>
 686     <thead>
 687      <row>
 688       <entry>Name</entry>
 689       <entry>Type</entry>
 690       <entry>References</entry>
 691       <entry>Description</entry>
 692      </row>
 693     </thead>
 694     <tbody>
 695
 696      <row>
 697       <entry><structfield>amprocfamily</structfield></entry>
 698       <entry><type>oid</type></entry>
 699       <entry><literal><link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link>.oid</literal></entry>
 700       <entry>The operator family this entry is for</entry>
 701      </row>
 702
 703      <row>
 704       <entry><structfield>amproclefttype</structfield></entry>
 705       <entry><type>oid</type></entry>
 706       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 707       <entry>Left-hand input data type of associated operator</entry>
 708      </row>
 709
 710      <row>
 711       <entry><structfield>amprocrighttype</structfield></entry>
 712       <entry><type>oid</type></entry>
 713       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 714       <entry>Right-hand input data type of associated operator</entry>
 715      </row>
 716
 717      <row>
 718       <entry><structfield>amprocnum</structfield></entry>
 719       <entry><type>int2</type></entry>
 720       <entry></entry>
 721       <entry>Support procedure number</entry>
 722      </row>
 723
 724      <row>
 725       <entry><structfield>amproc</structfield></entry>
 726       <entry><type>regproc</type></entry>
 727       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 728       <entry>OID of the procedure</entry>
 729      </row>
 730
 731     </tbody>
 732    </tgroup>
 733   </table>
 734
 735   <para>
 736    The usual interpretation of the
 737    <structfield>amproclefttype</> and <structfield>amprocrighttype</> fields
 738    is that they identify the left and right input types of the operator(s)
 739    that a particular support procedure supports.  For some access methods
 740    these match the input data type(s) of the support procedure itself, for
 741    others not.  There is a notion of <quote>default</> support procedures for
 742    an index, which are those with <structfield>amproclefttype</> and
 743    <structfield>amprocrighttype</> both equal to the index opclass's
 744    <structfield>opcintype</>.
 745   </para>
 746
 747  </sect1>
 748
 749
 750  <sect1 id="catalog-pg-attrdef">
 751   <title><structname>pg_attrdef</structname></title>
 752
 753   <indexterm zone="catalog-pg-attrdef">
 754    <primary>pg_attrdef</primary>
 755   </indexterm>
 756
 757   <para>
 758    The catalog <structname>pg_attrdef</structname> stores column default values.  The main information
 759    about columns is stored in <structname>pg_attribute</structname>
 760    (see below).  Only columns that explicitly specify a default value
 761    (when the table is created or the column is added) will have an
 762    entry here.
 763   </para>
 764
 765   <table>
 766    <title><structname>pg_attrdef</> Columns</title>
 767
 768    <tgroup cols=4>
 769     <thead>
 770      <row>
 771       <entry>Name</entry>
 772       <entry>Type</entry>
 773       <entry>References</entry>
 774       <entry>Description</entry>
 775      </row>
 776     </thead>
 777
 778     <tbody>
 779      <row>
 780       <entry><structfield>adrelid</structfield></entry>
 781       <entry><type>oid</type></entry>
 782       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
 783       <entry>The table this column belongs to</entry>
 784      </row>
 785
 786      <row>
 787       <entry><structfield>adnum</structfield></entry>
 788       <entry><type>int2</type></entry>
 789       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</literal></entry>
 790       <entry>The number of the column</entry>
 791      </row>
 792
 793      <row>
 794       <entry><structfield>adbin</structfield></entry>
 795       <entry><type>text</type></entry>
 796       <entry></entry>
 797       <entry>The internal representation of the column default value</entry>
 798      </row>
 799
 800      <row>
 801       <entry><structfield>adsrc</structfield></entry>
 802       <entry><type>text</type></entry>
 803       <entry></entry>
 804       <entry>A human-readable representation of the default value</entry>
 805      </row>
 806     </tbody>
 807    </tgroup>
 808   </table>
 809
 810    <para>
 811     The <structfield>adsrc</structfield> field is historical, and is best
 812     not used, because it does not track outside changes that might affect
 813     the representation of the default value.  Reverse-compiling the
 814     <structfield>adbin</structfield> field (with <function>pg_get_expr</> for
 815     example) is a better way to display the default value.
 816    </para>
 817
 818  </sect1>
 819
 820
 821  <sect1 id="catalog-pg-attribute">
 822   <title><structname>pg_attribute</structname></title>
 823
 824   <indexterm zone="catalog-pg-attribute">
 825    <primary>pg_attribute</primary>
 826   </indexterm>
 827
 828   <para>
 829    The catalog <structname>pg_attribute</structname> stores information about
 830    table columns.  There will be exactly one
 831    <structname>pg_attribute</structname> row for every column in every
 832    table in the database.  (There will also be attribute entries for
 833    indexes, and indeed all objects that have <structname>pg_class</structname>
 834    entries.)
 835   </para>
 836
 837   <para>
 838    The term attribute is equivalent to column and is used for
 839    historical reasons.
 840   </para>
 841
 842   <table>
 843    <title><structname>pg_attribute</> Columns</title>
 844
 845    <tgroup cols=4>
 846     <thead>
 847      <row>
 848       <entry>Name</entry>
 849       <entry>Type</entry>
 850       <entry>References</entry>
 851       <entry>Description</entry>
 852      </row>
 853     </thead>
 854
 855     <tbody>
 856      <row>
 857       <entry><structfield>attrelid</structfield></entry>
 858       <entry><type>oid</type></entry>
 859       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
 860       <entry>The table this column belongs to</entry>
 861      </row>
 862
 863      <row>
 864       <entry><structfield>attname</structfield></entry>
 865       <entry><type>name</type></entry>
 866       <entry></entry>
 867       <entry>The column name</entry>
 868      </row>
 869
 870      <row>
 871       <entry><structfield>atttypid</structfield></entry>
 872       <entry><type>oid</type></entry>
 873       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 874       <entry>The data type of this column</entry>
 875      </row>
 876
 877      <row>
 878       <entry><structfield>attstattarget</structfield></entry>
 879       <entry><type>int4</type></entry>
 880       <entry></entry>
 881       <entry>
 882        <structfield>attstattarget</structfield> controls the level of detail
 883        of statistics accumulated for this column by
 884        <xref linkend="sql-analyze" endterm="sql-analyze-title">.
 885        A zero value indicates that no statistics should be collected.
 886        A negative value says to use the system default statistics target.
 887        The exact meaning of positive values is data type-dependent.
 888        For scalar data types, <structfield>attstattarget</structfield>
 889        is both the target number of <quote>most common values</quote>
 890        to collect, and the target number of histogram bins to create
 891       </entry>
 892      </row>
 893
 894      <row>
 895       <entry><structfield>attlen</structfield></entry>
 896       <entry><type>int2</type></entry>
 897       <entry></entry>
 898       <entry>
 899        A copy of <literal>pg_type.typlen</literal> of this column's
 900        type
 901       </entry>
 902      </row>
 903
 904      <row>
 905       <entry><structfield>attnum</structfield></entry>
 906       <entry><type>int2</type></entry>
 907       <entry></entry>
 908       <entry>
 909        The number of the column.  Ordinary columns are numbered from 1
 910        up.  System columns, such as <structfield>oid</structfield>,
 911        have (arbitrary) negative numbers
 912       </entry>
 913      </row>
 914
 915      <row>
 916       <entry><structfield>attndims</structfield></entry>
 917       <entry><type>int4</type></entry>
 918       <entry></entry>
 919       <entry>
 920        Number of dimensions, if the column is an array type; otherwise 0.
 921        (Presently, the number of dimensions of an array is not enforced,
 922        so any nonzero value effectively means <quote>it's an array</>)
 923       </entry>
 924      </row>
 925
 926      <row>
 927       <entry><structfield>attcacheoff</structfield></entry>
 928       <entry><type>int4</type></entry>
 929       <entry></entry>
 930       <entry>
 931        Always -1 in storage, but when loaded into a row descriptor
 932        in memory this might be updated to cache the offset of the attribute
 933        within the row
 934       </entry>
 935      </row>
 936
 937      <row>
 938       <entry><structfield>atttypmod</structfield></entry>
 939       <entry><type>int4</type></entry>
 940       <entry></entry>
 941       <entry>
 942        <structfield>atttypmod</structfield> records type-specific data
 943        supplied at table creation time (for example, the maximum
 944        length of a <type>varchar</type> column).  It is passed to
 945        type-specific input functions and length coercion functions.
 946        The value will generally be -1 for types that do not need <structfield>atttypmod</>
 947       </entry>
 948      </row>
 949
 950      <row>
 951       <entry><structfield>attbyval</structfield></entry>
 952       <entry><type>bool</type></entry>
 953       <entry></entry>
 954       <entry>
 955        A copy of <literal>pg_type.typbyval</> of this column's type
 956       </entry>
 957      </row>
 958
 959      <row>
 960       <entry><structfield>attstorage</structfield></entry>
 961       <entry><type>char</type></entry>
 962       <entry></entry>
 963       <entry>
 964        Normally a copy of <literal>pg_type.typstorage</> of this
 965        column's type.  For TOAST-able data types, this can be altered
 966        after column creation to control storage policy
 967       </entry>
 968      </row>
 969
 970      <row>
 971       <entry><structfield>attalign</structfield></entry>
 972       <entry><type>char</type></entry>
 973       <entry></entry>
 974       <entry>
 975        A copy of <literal>pg_type.typalign</> of this column's type
 976       </entry>
 977      </row>
 978
 979      <row>
 980       <entry><structfield>attnotnull</structfield></entry>
 981       <entry><type>bool</type></entry>
 982       <entry></entry>
 983       <entry>
 984        This represents a not-null constraint.  It is possible to
 985        change this column to enable or disable the constraint
 986       </entry>
 987      </row>
 988
 989      <row>
 990       <entry><structfield>atthasdef</structfield></entry>
 991       <entry><type>bool</type></entry>
 992       <entry></entry>
 993       <entry>
 994        This column has a default value, in which case there will be a
 995        corresponding entry in the <structname>pg_attrdef</structname>
 996        catalog that actually defines the value
 997       </entry>
 998      </row>
 999
1000      <row>
1001       <entry><structfield>attisdropped</structfield></entry>
1002       <entry><type>bool</type></entry>
1003       <entry></entry>
1004       <entry>
1005        This column has been dropped and is no longer valid.  A dropped
1006        column is still physically present in the table, but is
1007        ignored by the parser and so cannot be accessed via SQL
1008       </entry>
1009      </row>
1010
1011      <row>
1012       <entry><structfield>attislocal</structfield></entry>
1013       <entry><type>bool</type></entry>
1014       <entry></entry>
1015       <entry>
1016        This column is defined locally in the relation.  Note that a column can
1017        be locally defined and inherited simultaneously
1018       </entry>
1019      </row>
1020
1021      <row>
1022       <entry><structfield>attinhcount</structfield></entry>
1023       <entry><type>int4</type></entry>
1024       <entry></entry>
1025       <entry>
1026        The number of direct ancestors this column has.  A column with a
1027        nonzero number of ancestors cannot be dropped nor renamed
1028       </entry>
1029      </row>
1030
1031     </tbody>
1032    </tgroup>
1033   </table>
1034
1035   <para>
1036    In a dropped column's <structname>pg_attribute</structname> entry,
1037    <structfield>atttypid</structfield> is reset to zero, but
1038    <structfield>attlen</structfield> and the other fields copied from
1039    <structname>pg_type</> are still valid.  This arrangement is needed
1040    to cope with the situation where the dropped column's data type was
1041    later dropped, and so there is no <structname>pg_type</> row anymore.
1042    <structfield>attlen</structfield> and the other fields can be used
1043    to interpret the contents of a row of the table.
1044   </para>
1045  </sect1>
1046
1047
1048  <sect1 id="catalog-pg-authid">
1049   <title><structname>pg_authid</structname></title>
1050
1051   <indexterm zone="catalog-pg-authid">
1052    <primary>pg_authid</primary>
1053   </indexterm>
1054
1055   <para>
1056    The catalog <structname>pg_authid</structname> contains information about
1057    database authorization identifiers (roles).  A role subsumes the concepts
1058    of <quote>users</> and <quote>groups</>.  A user is essentially just a
1059    role with the <structfield>rolcanlogin</> flag set.  Any role (with or
1060    without <structfield>rolcanlogin</>) can have other roles as members; see
1061    <link linkend="catalog-pg-auth-members"><structname>pg_auth_members</structname></link>.
1062   </para>
1063
1064   <para>
1065    Since this catalog contains passwords, it must not be publicly readable.
1066    <link linkend="view-pg-roles"><structname>pg_roles</structname></link>
1067    is a publicly readable view on
1068    <structname>pg_authid</structname> that blanks out the password field.
1069   </para>
1070
1071   <para>
1072    <xref linkend="user-manag"> contains detailed information about user and
1073    privilege management.
1074   </para>
1075
1076   <para>
1077    Because user identities are cluster-wide,
1078    <structname>pg_authid</structname>
1079    is shared across all databases of a cluster: there is only one
1080    copy of <structname>pg_authid</structname> per cluster, not
1081    one per database.
1082   </para>
1083
1084   <table>
1085    <title><structname>pg_authid</> Columns</title>
1086
1087    <tgroup cols=3>
1088     <thead>
1089      <row>
1090       <entry>Name</entry>
1091       <entry>Type</entry>
1092       <entry>Description</entry>
1093      </row>
1094     </thead>
1095
1096     <tbody>
1097      <row>
1098       <entry><structfield>rolname</structfield></entry>
1099       <entry><type>name</type></entry>
1100       <entry>Role name</entry>
1101      </row>
1102
1103      <row>
1104       <entry><structfield>rolsuper</structfield></entry>
1105       <entry><type>bool</type></entry>
1106       <entry>Role has superuser privileges</entry>
1107      </row>
1108
1109      <row>
1110       <entry><structfield>rolinherit</structfield></entry>
1111       <entry><type>bool</type></entry>
1112       <entry>Role automatically inherits privileges of roles it is a
1113        member of</entry>
1114      </row>
1115
1116      <row>
1117       <entry><structfield>rolcreaterole</structfield></entry>
1118       <entry><type>bool</type></entry>
1119       <entry>Role can create more roles</entry>
1120      </row>
1121
1122      <row>
1123       <entry><structfield>rolcreatedb</structfield></entry>
1124       <entry><type>bool</type></entry>
1125       <entry>Role can create databases</entry>
1126      </row>
1127
1128      <row>
1129       <entry><structfield>rolcatupdate</structfield></entry>
1130       <entry><type>bool</type></entry>
1131       <entry>
1132        Role can update system catalogs directly.  (Even a superuser cannot do
1133        this unless this column is true)
1134       </entry>
1135      </row>
1136
1137      <row>
1138       <entry><structfield>rolcanlogin</structfield></entry>
1139       <entry><type>bool</type></entry>
1140       <entry>
1141        Role can log in. That is, this role can be given as the initial
1142        session authorization identifier
1143       </entry>
1144      </row>
1145
1146      <row>
1147       <entry><structfield>rolconnlimit</structfield></entry>
1148       <entry><type>int4</type></entry>
1149       <entry>
1150        For roles that can log in, this sets maximum number of concurrent
1151        connections this role can make.  -1 means no limit
1152       </entry>
1153      </row>
1154
1155      <row>
1156       <entry><structfield>rolpassword</structfield></entry>
1157       <entry><type>text</type></entry>
1158       <entry>Password (possibly encrypted); NULL if none</entry>
1159      </row>
1160
1161      <row>
1162       <entry><structfield>rolvaliduntil</structfield></entry>
1163       <entry><type>timestamptz</type></entry>
1164       <entry>Password expiry time (only used for password authentication);
1165        NULL if no expiration</entry>
1166      </row>
1167
1168      <row>
1169       <entry><structfield>rolconfig</structfield></entry>
1170       <entry><type>text[]</type></entry>
1171       <entry>Session defaults for run-time configuration variables</entry>
1172      </row>
1173     </tbody>
1174    </tgroup>
1175   </table>
1176
1177  </sect1>
1178
1179
1180  <sect1 id="catalog-pg-auth-members">
1181   <title><structname>pg_auth_members</structname></title>
1182
1183   <indexterm zone="catalog-pg-auth-members">
1184    <primary>pg_auth_members</primary>
1185   </indexterm>
1186
1187   <para>
1188    The catalog <structname>pg_auth_members</structname> shows the membership
1189    relations between roles.  Any non-circular set of relationships is allowed.
1190   </para>
1191
1192   <para>
1193    Because user identities are cluster-wide,
1194    <structname>pg_auth_members</structname>
1195    is shared across all databases of a cluster: there is only one
1196    copy of <structname>pg_auth_members</structname> per cluster, not
1197    one per database.
1198   </para>
1199
1200   <table>
1201    <title><structname>pg_auth_members</> Columns</title>
1202
1203    <tgroup cols=4>
1204     <thead>
1205      <row>
1206       <entry>Name</entry>
1207       <entry>Type</entry>
1208       <entry>References</entry>
1209       <entry>Description</entry>
1210      </row>
1211     </thead>
1212
1213     <tbody>
1214      <row>
1215       <entry><structfield>roleid</structfield></entry>
1216       <entry><type>oid</type></entry>
1217       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
1218       <entry>ID of a role that has a member</entry>
1219      </row>
1220
1221      <row>
1222       <entry><structfield>member</structfield></entry>
1223       <entry><type>oid</type></entry>
1224       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
1225       <entry>ID of a role that is a member of <structfield>roleid</></entry>
1226      </row>
1227
1228      <row>
1229       <entry><structfield>grantor</structfield></entry>
1230       <entry><type>oid</type></entry>
1231       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
1232       <entry>ID of the role that granted this membership</entry>
1233      </row>
1234
1235      <row>
1236       <entry><structfield>admin_option</structfield></entry>
1237       <entry><type>bool</type></entry>
1238       <entry></entry>
1239       <entry>True if <structfield>member</> can grant membership in
1240        <structfield>roleid</> to others</entry>
1241      </row>
1242     </tbody>
1243    </tgroup>
1244   </table>
1245
1246  </sect1>
1247
1248
1249  <sect1 id="catalog-pg-autovacuum">
1250   <title><structname>pg_autovacuum</structname></title>
1251
1252   <indexterm zone="catalog-pg-autovacuum">
1253    <primary>pg_autovacuum</primary>
1254   </indexterm>
1255
1256   <indexterm zone="catalog-pg-autovacuum">
1257    <primary>autovacuum</primary>
1258    <secondary>table-specific configuration</secondary>
1259   </indexterm>
1260
1261   <para>
1262    The catalog <structname>pg_autovacuum</structname> stores optional
1263    per-relation configuration parameters for the autovacuum daemon.
1264    If there is an entry here for a particular relation, the given
1265    parameters will be used for autovacuuming that table.  If no entry
1266    is present, the system-wide defaults will be used. For more information
1267    about the autovacuum daemon, see <xref linkend="autovacuum">.
1268   </para>
1269
1270   <note>
1271    <para>
1272     It is likely that <structname>pg_autovacuum</structname> will disappear
1273     in a future release, with the information instead being kept in
1274     <structname>pg_class</>.<structfield>reloptions</> entries.
1275    </para>
1276   </note>
1277
1278   <table>
1279    <title><structname>pg_autovacuum</> Columns</title>
1280
1281    <tgroup cols=4>
1282     <thead>
1283      <row>
1284       <entry>Name</entry>
1285       <entry>Type</entry>
1286       <entry>References</entry>
1287       <entry>Description</entry>
1288      </row>
1289     </thead>
1290
1291     <tbody>
1292      <row>
1293       <entry><structfield>vacrelid</structfield></entry>
1294       <entry><type>oid</type></entry>
1295       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
1296       <entry>The table this entry is for</entry>
1297      </row>
1298
1299      <row>
1300       <entry><structfield>enabled</structfield></entry>
1301       <entry><type>bool</type></entry>
1302       <entry></entry>
1303       <entry>If false, this table will not be autovacuumed, except
1304        to prevent transaction ID wraparound</entry>
1305      </row>
1306
1307      <row>
1308       <entry><structfield>vac_base_thresh</structfield></entry>
1309       <entry><type>integer</type></entry>
1310       <entry></entry>
1311       <entry>Minimum number of modified tuples before vacuum</entry>
1312      </row>
1313
1314      <row>
1315       <entry><structfield>vac_scale_factor</structfield></entry>
1316       <entry><type>float4</type></entry>
1317       <entry></entry>
1318       <entry>Multiplier for <structfield>reltuples</> to add to
1319        <structfield>vac_base_thresh</></entry>
1320      </row>
1321
1322      <row>
1323       <entry><structfield>anl_base_thresh</structfield></entry>
1324       <entry><type>integer</type></entry>
1325       <entry></entry>
1326       <entry>Minimum number of modified tuples before analyze</entry>
1327      </row>
1328
1329      <row>
1330       <entry><structfield>anl_scale_factor</structfield></entry>
1331       <entry><type>float4</type></entry>
1332       <entry></entry>
1333       <entry>Multiplier for <structfield>reltuples</> to add to
1334        <structfield>anl_base_thresh</></entry>
1335      </row>
1336
1337      <row>
1338       <entry><structfield>vac_cost_delay</structfield></entry>
1339       <entry><type>integer</type></entry>
1340       <entry></entry>
1341       <entry>Custom <varname>vacuum_cost_delay</> parameter</entry>
1342      </row>
1343
1344      <row>
1345       <entry><structfield>vac_cost_limit</structfield></entry>
1346       <entry><type>integer</type></entry>
1347       <entry></entry>
1348       <entry>Custom <varname>vacuum_cost_limit</> parameter</entry>
1349      </row>
1350
1351      <row>
1352       <entry><structfield>freeze_min_age</structfield></entry>
1353       <entry><type>integer</type></entry>
1354       <entry></entry>
1355       <entry>Custom <varname>vacuum_freeze_min_age</> parameter</entry>
1356      </row>
1357
1358      <row>
1359       <entry><structfield>freeze_max_age</structfield></entry>
1360       <entry><type>integer</type></entry>
1361       <entry></entry>
1362       <entry>Custom <varname>autovacuum_freeze_max_age</> parameter</entry>
1363      </row>
1364     </tbody>
1365    </tgroup>
1366   </table>
1367
1368   <para>
1369    The autovacuum daemon will initiate a <command>VACUUM</> operation
1370    on a particular table when the number of updated or deleted tuples
1371    exceeds <structfield>vac_base_thresh</structfield> plus
1372    <structfield>vac_scale_factor</structfield> times the number of
1373    live tuples currently estimated to be in the relation.
1374    Similarly, it will initiate an <command>ANALYZE</> operation
1375    when the number of inserted, updated or deleted tuples
1376    exceeds <structfield>anl_base_thresh</structfield> plus
1377    <structfield>anl_scale_factor</structfield> times the number of
1378    live tuples currently estimated to be in the relation.
1379   </para>
1380
1381   <para>
1382    Also, the autovacuum daemon will perform a <command>VACUUM</> operation
1383    to prevent transaction ID wraparound if the table's
1384    <structname>pg_class</>.<structfield>relfrozenxid</> field attains an age
1385    of more than <structfield>freeze_max_age</> transactions, whether the table
1386    has been changed or not, even if
1387    <structname>pg_autovacuum</>.<structfield>enabled</> is set to
1388    <literal>false</> for it.  The system will launch autovacuum to perform
1389    such <command>VACUUM</>s even if autovacuum is otherwise disabled.
1390    See <xref linkend="vacuum-for-wraparound"> for more about wraparound
1391    prevention.
1392   </para>
1393
1394   <para>
1395    Any of the numerical fields can contain <literal>-1</> (or indeed
1396    any negative value) to indicate that the system-wide default should
1397    be used for this particular value.  Observe that the
1398    <structfield>vac_cost_delay</> variable inherits its default value from the
1399    <xref linkend="guc-autovacuum-vacuum-cost-delay"> configuration parameter,
1400    or from <xref linkend="guc-vacuum-cost-delay"> if the former is set to a
1401    negative value.  The same applies to <structfield>vac_cost_limit</>.
1402    Also, autovacuum will ignore attempts to set a per-table
1403    <structfield>freeze_max_age</> larger than the system-wide setting (it can
1404    only be set smaller), and the <structfield>freeze_min_age</> value will be
1405    limited to half the system-wide <xref
1406    linkend="guc-autovacuum-freeze-max-age"> setting.  Note that while you
1407    can set <structfield>freeze_max_age</> very small, or even zero, this
1408    is usually unwise since it will force frequent vacuuming.
1409   </para>
1410
1411  </sect1>
1412
1413
1414  <sect1 id="catalog-pg-cast">
1415   <title><structname>pg_cast</structname></title>
1416
1417   <indexterm zone="catalog-pg-cast">
1418    <primary>pg_cast</primary>
1419   </indexterm>
1420
1421   <para>
1422    The catalog <structname>pg_cast</structname> stores data type conversion
1423    paths, both built-in paths and those defined with
1424    <xref linkend="sql-createcast" endterm="sql-createcast-title">.
1425   </para>
1426
1427   <para>
1428    It should be noted that <structname>pg_cast</structname> does not represent
1429    every type conversion that the system knows how to perform; only those that
1430    cannot be deduced from some generic rule.  For example, casting between a
1431    domain and its base type is not explicitly represented in
1432    <structname>pg_cast</structname>.  Another important exception is that
1433    <quote>automatic I/O conversion casts</>, those performed using a data
1434    type's own I/O functions to convert to or from <type>text</> or other
1435    string types, are not explicitly represented in
1436    <structname>pg_cast</structname>.
1437   </para>
1438
1439   <table>
1440    <title><structname>pg_cast</> Columns</title>
1441
1442    <tgroup cols=4>
1443     <thead>
1444      <row>
1445       <entry>Name</entry>
1446       <entry>Type</entry>
1447       <entry>References</entry>
1448       <entry>Description</entry>
1449      </row>
1450     </thead>
1451
1452     <tbody>
1453      <row>
1454       <entry><structfield>castsource</structfield></entry>
1455       <entry><type>oid</type></entry>
1456       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
1457       <entry>OID of the source data type</entry>
1458      </row>
1459
1460      <row>
1461       <entry><structfield>casttarget</structfield></entry>
1462       <entry><type>oid</type></entry>
1463       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
1464       <entry>OID of the target data type</entry>
1465      </row>
1466
1467      <row>
1468       <entry><structfield>castfunc</structfield></entry>
1469       <entry><type>oid</type></entry>
1470       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
1471       <entry>
1472        The OID of the function to use to perform this cast.  Zero is
1473        stored if the cast method doesn't require a function.
1474       </entry>
1475      </row>
1476
1477      <row>
1478       <entry><structfield>castcontext</structfield></entry>
1479       <entry><type>char</type></entry>
1480       <entry></entry>
1481       <entry>
1482        Indicates what contexts the cast can be invoked in.
1483        <literal>e</> means only as an explicit cast (using
1484        <literal>CAST</> or <literal>::</> syntax).
1485        <literal>a</> means implicitly in assignment
1486        to a target column, as well as explicitly.
1487        <literal>i</> means implicitly in expressions, as well as the
1488        other cases
1489       </entry>
1490      </row>
1491      <row>
1492       <entry><structfield>castmethod</structfield></entry>
1493       <entry><type>char</type></entry>
1494       <entry></entry>
1495       <entry>
1496        Indicates how the cast is performed.
1497        <literal>f</> means that the function specified in the <structfield>castfunc</> field is used.
1498        <literal>i</> means that the input/output functions are used.
1499        <literal>b</> means that the types are binary-coercible, thus no conversion is required
1500       </entry>
1501      </row>
1502     </tbody>
1503    </tgroup>
1504   </table>
1505
1506   <para>
1507    The cast functions listed in <structname>pg_cast</structname> must
1508    always take the cast source type as their first argument type, and
1509    return the cast destination type as their result type.  A cast
1510    function can have up to three arguments.  The second argument,
1511    if present, must be type <type>integer</>; it receives the type
1512    modifier associated with the destination type, or <literal>-1</>
1513    if there is none.  The third argument,
1514    if present, must be type <type>boolean</>; it receives <literal>true</>
1515    if the cast is an explicit cast, <literal>false</> otherwise.
1516   </para>
1517
1518   <para>
1519    It is legitimate to create a <structname>pg_cast</structname> entry
1520    in which the source and target types are the same, if the associated
1521    function takes more than one argument.  Such entries represent
1522    <quote>length coercion functions</> that coerce values of the type
1523    to be legal for a particular type modifier value.
1524   </para>
1525
1526   <para>
1527    When a <structname>pg_cast</structname> entry has different source and
1528    target types and a function that takes more than one argument, it
1529    represents converting from one type to another and applying a length
1530    coercion in a single step.  When no such entry is available, coercion
1531    to a type that uses a type modifier involves two steps, one to
1532    convert between data types and a second to apply the modifier.
1533   </para>
1534  </sect1>
1535
1536  <sect1 id="catalog-pg-class">
1537   <title><structname>pg_class</structname></title>
1538
1539   <indexterm zone="catalog-pg-class">
1540    <primary>pg_class</primary>
1541   </indexterm>
1542
1543   <para>
1544    The catalog <structname>pg_class</structname> catalogs tables and most
1545    everything else that has columns or is otherwise similar to a
1546    table.  This includes indexes (but see also
1547    <structname>pg_index</structname>), sequences, views, composite types,
1548    and TOAST tables; see <structfield>relkind</>.
1549    Below, when we mean all of these
1550    kinds of objects we speak of <quote>relations</quote>.  Not all
1551    columns are meaningful for all relation types.
1552   </para>
1553
1554   <table>
1555    <title><structname>pg_class</> Columns</title>
1556
1557    <tgroup cols=4>
1558     <thead>
1559      <row>
1560       <entry>Name</entry>
1561       <entry>Type</entry>
1562       <entry>References</entry>
1563       <entry>Description</entry>
1564      </row>
1565     </thead>
1566
1567     <tbody>
1568      <row>
1569       <entry><structfield>relname</structfield></entry>
1570       <entry><type>name</type></entry>
1571       <entry></entry>
1572       <entry>Name of the table, index, view, etc.</entry>
1573      </row>
1574
1575      <row>
1576       <entry><structfield>relnamespace</structfield></entry>
1577       <entry><type>oid</type></entry>
1578       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
1579       <entry>
1580        The OID of the namespace that contains this relation
1581       </entry>
1582      </row>
1583
1584      <row>
1585       <entry><structfield>reltype</structfield></entry>
1586       <entry><type>oid</type></entry>
1587       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
1588       <entry>
1589        The OID of the data type that corresponds to this table's row type,
1590        if any (zero for indexes, which have no <structname>pg_type</> entry)
1591       </entry>
1592      </row>
1593
1594      <row>
1595       <entry><structfield>relowner</structfield></entry>
1596       <entry><type>oid</type></entry>
1597       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
1598       <entry>Owner of the relation</entry>
1599      </row>
1600
1601      <row>
1602       <entry><structfield>relam</structfield></entry>
1603       <entry><type>oid</type></entry>
1604       <entry><literal><link linkend="catalog-pg-am"><structname>pg_am</structname></link>.oid</literal></entry>
1605       <entry>If this is an index, the access method used (B-tree, hash, etc.)</entry>
1606      </row>
1607
1608      <row>
1609       <entry><structfield>relfilenode</structfield></entry>
1610       <entry><type>oid</type></entry>
1611       <entry></entry>
1612       <entry>Name of the on-disk file of this relation; 0 if none</entry>
1613      </row>
1614
1615      <row>
1616       <entry><structfield>reltablespace</structfield></entry>
1617       <entry><type>oid</type></entry>
1618       <entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.oid</literal></entry>
1619       <entry>
1620        The tablespace in which this relation is stored.  If zero,
1621        the database's default tablespace is implied.  (Not meaningful
1622        if the relation has no on-disk file.)
1623       </entry>
1624      </row>
1625
1626      <row>
1627       <entry><structfield>relpages</structfield></entry>
1628       <entry><type>int4</type></entry>
1629       <entry></entry>
1630       <entry>
1631        Size of the on-disk representation of this table in pages (of size
1632        <symbol>BLCKSZ</symbol>).  This is only an estimate used by the
1633        planner.  It is updated by <command>VACUUM</command>,
1634        <command>ANALYZE</command>, and a few DDL commands such as
1635        <command>CREATE INDEX</command>
1636       </entry>
1637      </row>
1638
1639      <row>
1640       <entry><structfield>reltuples</structfield></entry>
1641       <entry><type>float4</type></entry>
1642       <entry></entry>
1643       <entry>
1644        Number of rows in the table.  This is only an estimate used by the
1645        planner.  It is updated by <command>VACUUM</command>,
1646        <command>ANALYZE</command>, and a few DDL commands such as
1647        <command>CREATE INDEX</command>
1648       </entry>
1649      </row>
1650
1651      <row>
1652       <entry><structfield>reltoastrelid</structfield></entry>
1653       <entry><type>oid</type></entry>
1654       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
1655       <entry>
1656        OID of the TOAST table associated with this table, 0 if none.  The
1657        TOAST table stores large attributes <quote>out of line</quote> in a
1658        secondary table
1659       </entry>
1660      </row>
1661
1662      <row>
1663       <entry><structfield>reltoastidxid</structfield></entry>
1664       <entry><type>oid</type></entry>
1665       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
1666       <entry>
1667        For a TOAST table, the OID of its index.  0 if not a TOAST table
1668       </entry>
1669      </row>
1670
1671      <row>
1672       <entry><structfield>relhasindex</structfield></entry>
1673       <entry><type>bool</type></entry>
1674       <entry></entry>
1675       <entry>
1676        True if this is a table and it has (or recently had) any
1677        indexes. This is set by <command>CREATE INDEX</command>, but
1678        not cleared immediately by <command>DROP INDEX</command>.
1679        <command>VACUUM</command> clears <structfield>relhasindex</> if it finds the
1680        table has no indexes
1681       </entry>
1682      </row>
1683
1684      <row>
1685       <entry><structfield>relisshared</structfield></entry>
1686       <entry><type>bool</type></entry>
1687       <entry></entry>
1688       <entry>
1689        True if this table is shared across all databases in the cluster.  Only
1690        certain system catalogs (such as <structname>pg_database</structname>)
1691        are shared
1692       </entry>
1693      </row>
1694
1695      <row>
1696       <entry><structfield>relkind</structfield></entry>
1697       <entry><type>char</type></entry>
1698       <entry></entry>
1699       <entry>
1700        <literal>r</> = ordinary table, <literal>i</> = index,
1701        <literal>S</> = sequence, <literal>v</> = view, <literal>c</> =
1702        composite type, <literal>t</> = TOAST
1703        table
1704       </entry>
1705      </row>
1706
1707      <row>
1708       <entry><structfield>relnatts</structfield></entry>
1709       <entry><type>int2</type></entry>
1710       <entry></entry>
1711       <entry>
1712        Number of user columns in the relation (system columns not
1713        counted).  There must be this many corresponding entries in
1714        <structname>pg_attribute</structname>.  See also
1715        <literal>pg_attribute.attnum</literal>
1716       </entry>
1717      </row>
1718
1719      <row>
1720       <entry><structfield>relchecks</structfield></entry>
1721       <entry><type>int2</type></entry>
1722       <entry></entry>
1723       <entry>
1724        Number of check constraints on the table; see
1725        <link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link> catalog
1726       </entry>
1727      </row>
1728
1729      <row>
1730       <entry><structfield>relhasoids</structfield></entry>
1731       <entry><type>bool</type></entry>
1732       <entry></entry>
1733       <entry>
1734        True if we generate an OID for each row of the relation
1735       </entry>
1736      </row>
1737
1738      <row>
1739       <entry><structfield>relhaspkey</structfield></entry>
1740       <entry><type>bool</type></entry>
1741       <entry></entry>
1742       <entry>
1743        True if the table has (or once had) a primary key
1744       </entry>
1745      </row>
1746
1747      <row>
1748       <entry><structfield>relhasrules</structfield></entry>
1749       <entry><type>bool</type></entry>
1750       <entry></entry>
1751       <entry>
1752        True if table has (or once had) rules; see
1753        <link linkend="catalog-pg-rewrite"><structname>pg_rewrite</structname></link> catalog
1754       </entry>
1755      </row>
1756
1757      <row>
1758       <entry><structfield>relhastriggers</structfield></entry>
1759       <entry><type>bool</type></entry>
1760       <entry></entry>
1761       <entry>
1762        True if table has (or once had) triggers; see
1763        <link linkend="catalog-pg-trigger"><structname>pg_trigger</structname></link> catalog
1764       </entry>
1765      </row>
1766
1767      <row>
1768       <entry><structfield>relhassubclass</structfield></entry>
1769       <entry><type>bool</type></entry>
1770       <entry></entry>
1771       <entry>True if table has (or once had) any inheritance children</entry>
1772      </row>
1773
1774      <row>
1775       <entry><structfield>relfrozenxid</structfield></entry>
1776       <entry><type>xid</type></entry>
1777       <entry></entry>
1778       <entry>
1779        All transaction IDs before this one have been replaced with a permanent
1780        (<quote>frozen</>) transaction ID in this table.  This is used to track
1781        whether the table needs to be vacuumed in order to prevent transaction
1782        ID wraparound or to allow <literal>pg_clog</> to be shrunk.  Zero
1783        (<symbol>InvalidTransactionId</symbol>) if the relation is not a table
1784       </entry>
1785      </row>
1786
1787      <row>
1788       <entry><structfield>relacl</structfield></entry>
1789       <entry><type>aclitem[]</type></entry>
1790       <entry></entry>
1791       <entry>
1792        Access privileges; see
1793        <xref linkend="sql-grant" endterm="sql-grant-title"> and
1794        <xref linkend="sql-revoke" endterm="sql-revoke-title">
1795        for details
1796       </entry>
1797      </row>
1798
1799      <row>
1800       <entry><structfield>reloptions</structfield></entry>
1801       <entry><type>text[]</type></entry>
1802       <entry></entry>
1803       <entry>
1804        Access-method-specific options, as <quote>keyword=value</> strings
1805       </entry>
1806      </row>
1807     </tbody>
1808    </tgroup>
1809   </table>
1810  </sect1>
1811
1812  <sect1 id="catalog-pg-constraint">
1813   <title><structname>pg_constraint</structname></title>
1814
1815   <indexterm zone="catalog-pg-constraint">
1816    <primary>pg_constraint</primary>
1817   </indexterm>
1818
1819   <para>
1820    The catalog <structname>pg_constraint</structname> stores check, primary key, unique, and foreign
1821    key constraints on tables.  (Column constraints are not treated
1822    specially.  Every column constraint is equivalent to some table
1823    constraint.)  Not-null constraints are represented in the
1824    <structname>pg_attribute</> catalog.
1825   </para>
1826
1827   <para>
1828    Check constraints on domains are stored here, too.
1829   </para>
1830
1831   <table>
1832    <title><structname>pg_constraint</> Columns</title>
1833
1834    <tgroup cols=4>
1835     <thead>
1836      <row>
1837       <entry>Name</entry>
1838       <entry>Type</entry>
1839       <entry>References</entry>
1840       <entry>Description</entry>
1841      </row>
1842     </thead>
1843
1844     <tbody>
1845      <row>
1846       <entry><structfield>conname</structfield></entry>
1847       <entry><type>name</type></entry>
1848       <entry></entry>
1849       <entry>Constraint name (not necessarily unique!)</entry>
1850      </row>
1851
1852      <row>
1853       <entry><structfield>connamespace</structfield></entry>
1854       <entry><type>oid</type></entry>
1855       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
1856       <entry>
1857        The OID of the namespace that contains this constraint
1858       </entry>
1859      </row>
1860
1861      <row>
1862       <entry><structfield>contype</structfield></entry>
1863       <entry><type>char</type></entry>
1864       <entry></entry>
1865       <entry>
1866         <literal>c</> = check constraint,
1867         <literal>f</> = foreign key constraint,
1868         <literal>p</> = primary key constraint,
1869         <literal>u</> = unique constraint
1870       </entry>
1871      </row>
1872
1873      <row>
1874       <entry><structfield>condeferrable</structfield></entry>
1875       <entry><type>bool</type></entry>
1876       <entry></entry>
1877       <entry>Is the constraint deferrable?</entry>
1878      </row>
1879
1880      <row>
1881       <entry><structfield>condeferred</structfield></entry>
1882       <entry><type>bool</type></entry>
1883       <entry></entry>
1884       <entry>Is the constraint deferred by default?</entry>
1885      </row>
1886
1887      <row>
1888       <entry><structfield>conrelid</structfield></entry>
1889       <entry><type>oid</type></entry>
1890       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
1891       <entry>The table this constraint is on; 0 if not a table constraint</entry>
1892      </row>
1893
1894      <row>
1895       <entry><structfield>contypid</structfield></entry>
1896       <entry><type>oid</type></entry>
1897       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
1898       <entry>The domain this constraint is on; 0 if not a domain constraint</entry>
1899      </row>
1900
1901      <row>
1902       <entry><structfield>confrelid</structfield></entry>
1903       <entry><type>oid</type></entry>
1904       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
1905       <entry>If a foreign key, the referenced table; else 0</entry>
1906      </row>
1907
1908      <row>
1909       <entry><structfield>confupdtype</structfield></entry>
1910       <entry><type>char</type></entry>
1911       <entry></entry>
1912       <entry>Foreign key update action code:
1913             <literal>a</> = no action,
1914             <literal>r</> = restrict,
1915             <literal>c</> = cascade,
1916             <literal>n</> = set null,
1917             <literal>d</> = set default
1918           </entry>
1919      </row>
1920
1921      <row>
1922       <entry><structfield>confdeltype</structfield></entry>
1923       <entry><type>char</type></entry>
1924       <entry></entry>
1925       <entry>Foreign key deletion action code:
1926             <literal>a</> = no action,
1927             <literal>r</> = restrict,
1928             <literal>c</> = cascade,
1929             <literal>n</> = set null,
1930             <literal>d</> = set default
1931           </entry>
1932      </row>
1933
1934      <row>
1935       <entry><structfield>confmatchtype</structfield></entry>
1936       <entry><type>char</type></entry>
1937       <entry></entry>
1938       <entry>Foreign key match type:
1939             <literal>f</> = full,
1940             <literal>p</> = partial,
1941             <literal>u</> = simple (unspecified)
1942           </entry>
1943      </row>
1944
1945      <row>
1946       <entry><structfield>conislocal</structfield></entry>
1947       <entry><type>bool</type></entry>
1948       <entry></entry>
1949       <entry>
1950        This constraint is defined locally in the relation.  Note that a
1951        constraint can be locally defined and inherited simultaneously
1952       </entry>
1953      </row>
1954
1955      <row>
1956       <entry><structfield>coninhcount</structfield></entry>
1957       <entry><type>int4</type></entry>
1958       <entry></entry>
1959       <entry>
1960        The number of direct ancestors this constraint has.  A constraint with
1961        a nonzero number of ancestors cannot be dropped nor renamed
1962       </entry>
1963      </row>
1964
1965      <row>
1966       <entry><structfield>conkey</structfield></entry>
1967       <entry><type>int2[]</type></entry>
1968       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</></entry>
1969       <entry>If a table constraint, list of columns which the constraint constrains</entry>
1970      </row>
1971
1972      <row>
1973       <entry><structfield>confkey</structfield></entry>
1974       <entry><type>int2[]</type></entry>
1975       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</></entry>
1976       <entry>If a foreign key, list of the referenced columns</entry>
1977      </row>
1978
1979      <row>
1980       <entry><structfield>conpfeqop</structfield></entry>
1981       <entry><type>oid[]</type></entry>
1982       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</></entry>
1983       <entry>If a foreign key, list of the equality operators for PK = FK comparisons</entry>
1984      </row>
1985
1986      <row>
1987       <entry><structfield>conppeqop</structfield></entry>
1988       <entry><type>oid[]</type></entry>
1989       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</></entry>
1990       <entry>If a foreign key, list of the equality operators for PK = PK comparisons</entry>
1991      </row>
1992
1993      <row>
1994       <entry><structfield>conffeqop</structfield></entry>
1995       <entry><type>oid[]</type></entry>
1996       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</></entry>
1997       <entry>If a foreign key, list of the equality operators for FK = FK comparisons</entry>
1998      </row>
1999
2000      <row>
2001       <entry><structfield>conbin</structfield></entry>
2002       <entry><type>text</type></entry>
2003       <entry></entry>
2004       <entry>If a check constraint, an internal representation of the expression</entry>
2005      </row>
2006
2007      <row>
2008       <entry><structfield>consrc</structfield></entry>
2009       <entry><type>text</type></entry>
2010       <entry></entry>
2011       <entry>If a check constraint, a human-readable representation of the expression</entry>
2012      </row>
2013     </tbody>
2014    </tgroup>
2015   </table>
2016
2017   <note>
2018    <para>
2019     <structfield>consrc</structfield> is not updated when referenced objects
2020     change; for example, it won't track renaming of columns.  Rather than
2021     relying on this field, it's best to use <function>pg_get_constraintdef()</>
2022     to extract the definition of a check constraint.
2023    </para>
2024   </note>
2025
2026   <note>
2027    <para>
2028     <literal>pg_class.relchecks</literal> needs to agree with the
2029     number of check-constraint entries found in this table for each
2030     relation.
2031    </para>
2032   </note>
2033
2034  </sect1>
2035
2036  <sect1 id="catalog-pg-conversion">
2037   <title><structname>pg_conversion</structname></title>
2038
2039   <indexterm zone="catalog-pg-conversion">
2040    <primary>pg_conversion</primary>
2041   </indexterm>
2042
2043   <para>
2044    The catalog <structname>pg_conversion</structname> describes the
2045    available encoding conversion procedures.  See
2046    <xref linkend="sql-createconversion" endterm="sql-createconversion-title">
2047    for more information.
2048   </para>
2049
2050   <table>
2051    <title><structname>pg_conversion</> Columns</title>
2052
2053    <tgroup cols=4>
2054     <thead>
2055      <row>
2056       <entry>Name</entry>
2057       <entry>Type</entry>
2058       <entry>References</entry>
2059       <entry>Description</entry>
2060      </row>
2061     </thead>
2062
2063     <tbody>
2064      <row>
2065       <entry><structfield>conname</structfield></entry>
2066       <entry><type>name</type></entry>
2067       <entry></entry>
2068       <entry>Conversion name (unique within a namespace)</entry>
2069      </row>
2070
2071      <row>
2072       <entry><structfield>connamespace</structfield></entry>
2073       <entry><type>oid</type></entry>
2074       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
2075       <entry>
2076        The OID of the namespace that contains this conversion
2077       </entry>
2078      </row>
2079
2080      <row>
2081       <entry><structfield>conowner</structfield></entry>
2082       <entry><type>oid</type></entry>
2083       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
2084       <entry>Owner of the conversion</entry>
2085      </row>
2086
2087      <row>
2088       <entry><structfield>conforencoding</structfield></entry>
2089       <entry><type>int4</type></entry>
2090       <entry></entry>
2091       <entry>Source encoding ID</entry>
2092      </row>
2093
2094      <row>
2095       <entry><structfield>contoencoding</structfield></entry>
2096       <entry><type>int4</type></entry>
2097       <entry></entry>
2098       <entry>Destination encoding ID</entry>
2099      </row>
2100
2101      <row>
2102       <entry><structfield>conproc</structfield></entry>
2103       <entry><type>regproc</type></entry>
2104       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
2105       <entry>Conversion procedure</entry>
2106      </row>
2107
2108      <row>
2109       <entry><structfield>condefault</structfield></entry>
2110       <entry><type>bool</type></entry>
2111       <entry></entry>
2112       <entry>True if this is the default conversion</entry>
2113      </row>
2114
2115     </tbody>
2116    </tgroup>
2117   </table>
2118
2119  </sect1>
2120
2121  <sect1 id="catalog-pg-database">
2122   <title><structname>pg_database</structname></title>
2123
2124   <indexterm zone="catalog-pg-database">
2125    <primary>pg_database</primary>
2126   </indexterm>
2127
2128   <para>
2129    The catalog <structname>pg_database</structname> stores information about
2130    the available databases.  Databases are created with the <xref
2131    linkend="sql-createdatabase" endterm="sql-createdatabase-title"> command.
2132    Consult <xref linkend="managing-databases"> for details about the meaning
2133    of some of the parameters.
2134   </para>
2135
2136   <para>
2137    Unlike most system catalogs, <structname>pg_database</structname>
2138    is shared across all databases of a cluster: there is only one
2139    copy of <structname>pg_database</structname> per cluster, not
2140    one per database.
2141   </para>
2142
2143   <table>
2144    <title><structname>pg_database</> Columns</title>
2145
2146    <tgroup cols=4>
2147     <thead>
2148      <row>
2149       <entry>Name</entry>
2150       <entry>Type</entry>
2151       <entry>References</entry>
2152       <entry>Description</entry>
2153      </row>
2154     </thead>
2155
2156     <tbody>
2157      <row>
2158       <entry><structfield>datname</structfield></entry>
2159       <entry><type>name</type></entry>
2160       <entry></entry>
2161       <entry>Database name</entry>
2162      </row>
2163
2164      <row>
2165       <entry><structfield>datdba</structfield></entry>
2166       <entry><type>oid</type></entry>
2167       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
2168       <entry>Owner of the database, usually the user who created it</entry>
2169      </row>
2170
2171      <row>
2172       <entry><structfield>encoding</structfield></entry>
2173       <entry><type>int4</type></entry>
2174       <entry></entry>
2175       <entry>Character encoding for this database
2176           (<function>pg_encoding_to_char()</function> can translate
2177            this number to the encoding name)</entry>
2178      </row>
2179
2180      <row>
2181       <entry><structfield>datcollate</structfield></entry>
2182       <entry><type>name</type></entry>
2183       <entry></entry>
2184       <entry>LC_COLLATE for this database</entry>
2185      </row>
2186
2187      <row>
2188       <entry><structfield>datctype</structfield></entry>
2189       <entry><type>name</type></entry>
2190       <entry></entry>
2191       <entry>LC_CTYPE for this database</entry>
2192      </row>
2193
2194      <row>
2195       <entry><structfield>datistemplate</structfield></entry>
2196       <entry><type>bool</type></entry>
2197       <entry></entry>
2198       <entry>
2199        If true then this database can be used in the
2200        <literal>TEMPLATE</literal> clause of <command>CREATE
2201        DATABASE</command> to create a new database as a clone of
2202        this one
2203       </entry>
2204      </row>
2205
2206      <row>
2207       <entry><structfield>datallowconn</structfield></entry>
2208       <entry><type>bool</type></entry>
2209       <entry></entry>
2210       <entry>
2211        If false then no one can connect to this database.  This is
2212        used to protect the <literal>template0</> database from being altered
2213       </entry>
2214      </row>
2215
2216      <row>
2217       <entry><structfield>datconnlimit</structfield></entry>
2218       <entry><type>int4</type></entry>
2219       <entry></entry>
2220       <entry>
2221        Sets maximum number of concurrent connections that can be made
2222        to this database.  -1 means no limit
2223       </entry>
2224      </row>
2225
2226      <row>
2227       <entry><structfield>datlastsysoid</structfield></entry>
2228       <entry><type>oid</type></entry>
2229       <entry></entry>
2230       <entry>
2231        Last system OID in the database; useful
2232        particularly to <application>pg_dump</application>
2233       </entry>
2234      </row>
2235
2236      <row>
2237       <entry><structfield>datfrozenxid</structfield></entry>
2238       <entry><type>xid</type></entry>
2239       <entry></entry>
2240       <entry>
2241        All transaction IDs before this one have been replaced with a permanent
2242        (<quote>frozen</>) transaction ID in this database.  This is used to
2243        track whether the database needs to be vacuumed in order to prevent
2244        transaction ID wraparound or to allow <literal>pg_clog</> to be shrunk.
2245        It is the minimum of the per-table
2246        <structname>pg_class</>.<structfield>relfrozenxid</> values
2247       </entry>
2248      </row>
2249
2250      <row>
2251       <entry><structfield>dattablespace</structfield></entry>
2252       <entry><type>oid</type></entry>
2253       <entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.oid</literal></entry>
2254       <entry>
2255        The default tablespace for the database.
2256        Within this database, all tables for which
2257        <structname>pg_class</>.<structfield>reltablespace</> is zero
2258        will be stored in this tablespace; in particular, all the non-shared
2259        system catalogs will be there
2260       </entry>
2261      </row>
2262
2263      <row>
2264       <entry><structfield>datconfig</structfield></entry>
2265       <entry><type>text[]</type></entry>
2266       <entry></entry>
2267       <entry>Session defaults for run-time configuration variables</entry>
2268      </row>
2269
2270      <row>
2271       <entry><structfield>datacl</structfield></entry>
2272       <entry><type>aclitem[]</type></entry>
2273       <entry></entry>
2274       <entry>
2275        Access privileges; see
2276        <xref linkend="sql-grant" endterm="sql-grant-title"> and
2277        <xref linkend="sql-revoke" endterm="sql-revoke-title">
2278        for details
2279       </entry>
2280      </row>
2281     </tbody>
2282    </tgroup>
2283   </table>
2284  </sect1>
2285
2286
2287  <sect1 id="catalog-pg-depend">
2288   <title><structname>pg_depend</structname></title>
2289
2290   <indexterm zone="catalog-pg-depend">
2291    <primary>pg_depend</primary>
2292   </indexterm>
2293
2294   <para>
2295    The catalog <structname>pg_depend</structname> records the dependency
2296    relationships between database objects.  This information allows
2297    <command>DROP</> commands to find which other objects must be dropped
2298    by <command>DROP CASCADE</> or prevent dropping in the <command>DROP
2299    RESTRICT</> case.
2300   </para>
2301
2302   <para>
2303    See also <link linkend="catalog-pg-shdepend"><structname>pg_shdepend</structname></link>,
2304    which performs a similar function for dependencies involving objects
2305    that are shared across a database cluster.
2306   </para>
2307
2308   <table>
2309    <title><structname>pg_depend</> Columns</title>
2310
2311    <tgroup cols=4>
2312     <thead>
2313      <row>
2314       <entry>Name</entry>
2315       <entry>Type</entry>
2316       <entry>References</entry>
2317       <entry>Description</entry>
2318      </row>
2319     </thead>
2320
2321     <tbody>
2322      <row>
2323       <entry><structfield>classid</structfield></entry>
2324       <entry><type>oid</type></entry>
2325       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
2326       <entry>The OID of the system catalog the dependent object is in</entry>
2327      </row>
2328
2329      <row>
2330       <entry><structfield>objid</structfield></entry>
2331       <entry><type>oid</type></entry>
2332       <entry>any OID column</entry>
2333       <entry>The OID of the specific dependent object</entry>
2334      </row>
2335
2336      <row>
2337       <entry><structfield>objsubid</structfield></entry>
2338       <entry><type>int4</type></entry>
2339       <entry></entry>
2340       <entry>
2341        For a table column, this is the column number (the
2342        <structfield>objid</> and <structfield>classid</> refer to the
2343        table itself).  For all other object types, this column is
2344        zero
2345       </entry>
2346      </row>
2347
2348      <row>
2349       <entry><structfield>refclassid</structfield></entry>
2350       <entry><type>oid</type></entry>
2351       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
2352       <entry>The OID of the system catalog the referenced object is in</entry>
2353      </row>
2354
2355      <row>
2356       <entry><structfield>refobjid</structfield></entry>
2357       <entry><type>oid</type></entry>
2358       <entry>any OID column</entry>
2359       <entry>The OID of the specific referenced object</entry>
2360      </row>
2361
2362      <row>
2363       <entry><structfield>refobjsubid</structfield></entry>
2364       <entry><type>int4</type></entry>
2365       <entry></entry>
2366       <entry>
2367        For a table column, this is the column number (the
2368        <structfield>refobjid</> and <structfield>refclassid</> refer
2369        to the table itself).  For all other object types, this column
2370        is zero
2371       </entry>
2372      </row>
2373
2374      <row>
2375       <entry><structfield>deptype</structfield></entry>
2376       <entry><type>char</type></entry>
2377       <entry></entry>
2378       <entry>
2379        A code defining the specific semantics of this dependency relationship; see text
2380       </entry>
2381      </row>
2382
2383     </tbody>
2384    </tgroup>
2385   </table>
2386
2387   <para>
2388    In all cases, a <structname>pg_depend</structname> entry indicates that the
2389    referenced object cannot be dropped without also dropping the dependent
2390    object.  However, there are several subflavors identified by
2391    <structfield>deptype</>:
2392
2393    <variablelist>
2394     <varlistentry>
2395      <term><symbol>DEPENDENCY_NORMAL</> (<literal>n</>)</term>
2396      <listitem>
2397       <para>
2398        A normal relationship between separately-created objects.  The
2399        dependent object can be dropped without affecting the
2400        referenced object.  The referenced object can only be dropped
2401        by specifying <literal>CASCADE</>, in which case the dependent
2402        object is dropped, too.  Example: a table column has a normal
2403        dependency on its data type.
2404       </para>
2405      </listitem>
2406     </varlistentry>
2407
2408     <varlistentry>
2409      <term><symbol>DEPENDENCY_AUTO</> (<literal>a</>)</term>
2410      <listitem>
2411       <para>
2412        The dependent object can be dropped separately from the
2413        referenced object, and should be automatically dropped
2414        (regardless of <literal>RESTRICT</> or <literal>CASCADE</>
2415        mode) if the referenced object is dropped.  Example: a named
2416        constraint on a table is made autodependent on the table, so
2417        that it will go away if the table is dropped.
2418       </para>
2419      </listitem>
2420     </varlistentry>
2421
2422     <varlistentry>
2423      <term><symbol>DEPENDENCY_INTERNAL</> (<literal>i</>)</term>
2424      <listitem>
2425       <para>
2426        The dependent object was created as part of creation of the
2427        referenced object, and is really just a part of its internal
2428        implementation.  A <command>DROP</> of the dependent object
2429        will be disallowed outright (we'll tell the user to issue a
2430        <command>DROP</> against the referenced object, instead).  A
2431        <command>DROP</> of the referenced object will be propagated
2432        through to drop the dependent object whether
2433        <command>CASCADE</> is specified or not.  Example: a trigger
2434        that's created to enforce a foreign-key constraint is made
2435        internally dependent on the constraint's
2436        <structname>pg_constraint</> entry.
2437       </para>
2438      </listitem>
2439     </varlistentry>
2440
2441     <varlistentry>
2442      <term><symbol>DEPENDENCY_PIN</> (<literal>p</>)</term>
2443      <listitem>
2444       <para>
2445        There is no dependent object; this type of entry is a signal
2446        that the system itself depends on the referenced object, and so
2447        that object must never be deleted.  Entries of this type are
2448        created only by <command>initdb</command>.  The columns for the
2449        dependent object contain zeroes.
2450       </para>
2451      </listitem>
2452     </varlistentry>
2453    </variablelist>
2454
2455    Other dependency flavors might be needed in future.
2456   </para>
2457
2458  </sect1>
2459
2460
2461  <sect1 id="catalog-pg-description">
2462   <title><structname>pg_description</structname></title>
2463
2464   <indexterm zone="catalog-pg-description">
2465    <primary>pg_description</primary>
2466   </indexterm>
2467
2468   <para>
2469    The catalog <structname>pg_description</> stores optional descriptions
2470    (comments) for each database object.  Descriptions can be manipulated
2471    with the <xref linkend="sql-comment" endterm="sql-comment-title"> command and viewed with
2472    <application>psql</application>'s <literal>\d</literal> commands.
2473    Descriptions of many built-in system objects are provided in the initial
2474    contents of <structname>pg_description</structname>.
2475   </para>
2476
2477   <para>
2478    See also <link linkend="catalog-pg-shdescription"><structname>pg_shdescription</structname></link>,
2479    which performs a similar function for descriptions involving objects that
2480    are shared across a database cluster.
2481   </para>
2482
2483   <table>
2484    <title><structname>pg_description</> Columns</title>
2485
2486    <tgroup cols=4>
2487     <thead>
2488      <row>
2489       <entry>Name</entry>
2490       <entry>Type</entry>
2491       <entry>References</entry>
2492       <entry>Description</entry>
2493      </row>
2494     </thead>
2495
2496     <tbody>
2497      <row>
2498       <entry><structfield>objoid</structfield></entry>
2499       <entry><type>oid</type></entry>
2500       <entry>any OID column</entry>
2501       <entry>The OID of the object this description pertains to</entry>
2502      </row>
2503
2504      <row>
2505       <entry><structfield>classoid</structfield></entry>
2506       <entry><type>oid</type></entry>
2507       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
2508       <entry>The OID of the system catalog this object appears in</entry>
2509      </row>
2510
2511      <row>
2512       <entry><structfield>objsubid</structfield></entry>
2513       <entry><type>int4</type></entry>
2514       <entry></entry>
2515       <entry>
2516        For a comment on a table column, this is the column number (the
2517        <structfield>objoid</> and <structfield>classoid</> refer to
2518        the table itself).  For all other object types, this column is
2519        zero
2520       </entry>
2521      </row>
2522
2523      <row>
2524       <entry><structfield>description</structfield></entry>
2525       <entry><type>text</type></entry>
2526       <entry></entry>
2527       <entry>Arbitrary text that serves as the description of this object</entry>
2528      </row>
2529     </tbody>
2530    </tgroup>
2531   </table>
2532
2533  </sect1>
2534
2535
2536  <sect1 id="catalog-pg-enum">
2537   <title><structname>pg_enum</structname></title>
2538
2539   <indexterm zone="catalog-pg-enum">
2540    <primary>pg_enum</primary>
2541   </indexterm>
2542
2543   <para>
2544    The <structname>pg_enum</structname> catalog contains entries
2545    matching enum types to their associated values and labels. The
2546    internal representation of a given enum value is actually the OID
2547    of its associated row in <structname>pg_enum</structname>.  The
2548    OIDs for a particular enum type are guaranteed to be ordered in
2549    the way the type should sort, but there is no guarantee about the
2550    ordering of OIDs of unrelated enum types.
2551   </para>
2552
2553   <table>
2554    <title><structname>pg_enum</> Columns</title>
2555
2556    <tgroup cols=4>
2557     <thead>
2558      <row>
2559       <entry>Name</entry>
2560       <entry>Type</entry>
2561       <entry>References</entry>
2562       <entry>Description</entry>
2563      </row>
2564     </thead>
2565
2566     <tbody>
2567      <row>
2568       <entry><structfield>enumtypid</structfield></entry>
2569       <entry><type>oid</type></entry>
2570       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
2571       <entry>The OID of the <structname>pg_type</> entry owning this enum value</entry>
2572      </row>
2573
2574      <row>
2575       <entry><structfield>enumlabel</structfield></entry>
2576       <entry><type>name</type></entry>
2577       <entry></entry>
2578       <entry>The textual label for this enum value</entry>
2579      </row>
2580     </tbody>
2581    </tgroup>
2582   </table>
2583  </sect1>
2584
2585
2586  <sect1 id="catalog-pg-foreign-data-wrapper">
2587   <title><structname>pg_foreign_data_wrapper</structname></title>
2588
2589   <indexterm zone="catalog-pg-foreign-data-wrapper">
2590    <primary>pg_foreign_data_wrapper</primary>
2591   </indexterm>
2592
2593   <para>
2594    The catalog <structname>pg_foreign_data_wrapper</structname> stores
2595    foreign-data wrapper definitions.  A foreign-data wrapper is the
2596    mechanism by which external data, residing on foreign servers, is
2597    accessed.
2598   </para>
2599
2600   <table>
2601    <title><structname>pg_foreign_data_wrapper</> Columns</title>
2602
2603    <tgroup cols=4>
2604     <thead>
2605      <row>
2606       <entry>Name</entry>
2607       <entry>Type</entry>
2608       <entry>References</entry>
2609       <entry>Description</entry>
2610      </row>
2611     </thead>
2612
2613     <tbody>
2614      <row>
2615       <entry><structfield>fdwname</structfield></entry>
2616       <entry><type>name</type></entry>
2617       <entry></entry>
2618       <entry>Name of the foreign-data wrapper</entry>
2619      </row>
2620
2621      <row>
2622       <entry><structfield>fdwowner</structfield></entry>
2623       <entry><type>oid</type></entry>
2624       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
2625       <entry>Owner of the foreign-data wrapper</entry>
2626      </row>
2627
2628      <row>
2629       <entry><structfield>fdwlibrary</structfield></entry>
2630       <entry><type>text</type></entry>
2631       <entry></entry>
2632       <entry>File name of the library implementing this foreign-data wrapper</entry>
2633      </row>
2634
2635      <row>
2636       <entry><structfield>fdwacl</structfield></entry>
2637       <entry><type>aclitem[]</type></entry>
2638       <entry></entry>
2639       <entry>
2640        Access privileges; see
2641        <xref linkend="sql-grant" endterm="sql-grant-title"> and
2642        <xref linkend="sql-revoke" endterm="sql-revoke-title">
2643        for details
2644       </entry>
2645      </row>
2646
2647      <row>
2648       <entry><structfield>fdwoptions</structfield></entry>
2649       <entry><type>text[]</type></entry>
2650       <entry></entry>
2651       <entry>
2652        Foreign-data wrapper specific options, as <quote>keyword=value</> strings
2653       </entry>
2654      </row>
2655     </tbody>
2656    </tgroup>
2657   </table>
2658  </sect1>
2659
2660
2661  <sect1 id="catalog-pg-foreign-server">
2662   <title><structname>pg_foreign_server</structname></title>
2663
2664   <indexterm zone="catalog-pg-foreign-server">
2665    <primary>pg_foreign_server</primary>
2666   </indexterm>
2667
2668   <para>
2669    The catalog <structname>pg_foreign_server</structname> stores
2670    foreign server definitions.  A foreign server describes the
2671    connection to a remote server, managing external data.  Foreign
2672    servers are accessed via foreign-data wrappers.
2673   </para>
2674
2675   <table>
2676    <title><structname>pg_foreign_server</> Columns</title>
2677
2678    <tgroup cols=4>
2679     <thead>
2680      <row>
2681       <entry>Name</entry>
2682       <entry>Type</entry>
2683       <entry>References</entry>
2684       <entry>Description</entry>
2685      </row>
2686     </thead>
2687
2688     <tbody>
2689      <row>
2690       <entry><structfield>srvname</structfield></entry>
2691       <entry><type>name</type></entry>
2692       <entry></entry>
2693       <entry>Name of the foreign server</entry>
2694      </row>
2695
2696      <row>
2697       <entry><structfield>srvowner</structfield></entry>
2698       <entry><type>oid</type></entry>
2699       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
2700       <entry>Owner of the foreign server</entry>
2701      </row>
2702
2703      <row>
2704       <entry><structfield>srvfdw</structfield></entry>
2705       <entry><type>oid</type></entry>
2706       <entry><literal><link linkend="catalog-pg-foreign-data-wrapper"><structname>pg_foreign_data_wrapper</structname></link>.oid</literal></entry>
2707       <entry>The OID of the foreign-data wrapper of this foreign server</entry>
2708      </row>
2709
2710      <row>
2711       <entry><structfield>srvtype</structfield></entry>
2712       <entry><type>text</type></entry>
2713       <entry></entry>
2714       <entry>Type of the server (optional)</entry>
2715      </row>
2716
2717      <row>
2718       <entry><structfield>srvversion</structfield></entry>
2719       <entry><type>text</type></entry>
2720       <entry></entry>
2721       <entry>Version of the server (optional)</entry>
2722      </row>
2723
2724      <row>
2725       <entry><structfield>srvacl</structfield></entry>
2726       <entry><type>aclitem[]</type></entry>
2727       <entry></entry>
2728       <entry>
2729        Access privileges; see
2730        <xref linkend="sql-grant" endterm="sql-grant-title"> and
2731        <xref linkend="sql-revoke" endterm="sql-revoke-title">
2732        for details
2733       </entry>
2734      </row>
2735
2736      <row>
2737       <entry><structfield>srvoptions</structfield></entry>
2738       <entry><type>text[]</type></entry>
2739       <entry></entry>
2740       <entry>
2741        Foreign server specific options, as <quote>keyword=value</> strings.
2742       </entry>
2743      </row>
2744     </tbody>
2745    </tgroup>
2746   </table>
2747  </sect1>
2748
2749
2750  <sect1 id="catalog-pg-user-mapping">
2751   <title><structname>pg_user_mapping</structname></title>
2752
2753   <indexterm zone="catalog-pg-user-mapping">
2754    <primary>pg_user_mapping</primary>
2755   </indexterm>
2756
2757   <para>
2758    The catalog <structname>pg_user_mapping</structname> stores
2759    the mappings from local user to remote.  Access to this catalog is
2760    restricted from normal users, use the view
2761    <link linkend="view-pg-user-mappings"><structname>pg_user_mappings</structname></link>
2762    instead.
2763   </para>
2764
2765   <table>
2766    <title><structname>pg_user_mapping</> Columns</title>
2767
2768    <tgroup cols=4>
2769     <thead>
2770      <row>
2771       <entry>Name</entry>
2772       <entry>Type</entry>
2773       <entry>References</entry>
2774       <entry>Description</entry>
2775      </row>
2776     </thead>
2777
2778     <tbody>
2779      <row>
2780       <entry><structfield>umuser</structfield></entry>
2781       <entry><type>oid</type></entry>
2782       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
2783       <entry>OID of the local role being mapped, 0 if the user mapping is public</entry>
2784      </row>
2785
2786      <row>
2787       <entry><structfield>umserver</structfield></entry>
2788       <entry><type>oid</type></entry>
2789       <entry><literal><link linkend="catalog-pg-foreign-server"><structname>pg_foreign_server</structname></link>.oid</literal></entry>
2790       <entry>
2791        The OID of the foreign server that contains this mapping
2792       </entry>
2793      </row>
2794
2795      <row>
2796       <entry><structfield>umoptions</structfield></entry>
2797       <entry><type>text[]</type></entry>
2798       <entry></entry>
2799       <entry>
2800        User mapping specific options, as <quote>keyword=value</> strings.
2801       </entry>
2802      </row>
2803     </tbody>
2804    </tgroup>
2805   </table>
2806  </sect1>
2807
2808
2809  <sect1 id="catalog-pg-index">
2810   <title><structname>pg_index</structname></title>
2811
2812   <indexterm zone="catalog-pg-index">
2813    <primary>pg_index</primary>
2814   </indexterm>
2815
2816   <para>
2817    The catalog <structname>pg_index</structname> contains part of the information
2818    about indexes.  The rest is mostly in
2819    <structname>pg_class</structname>.
2820   </para>
2821
2822   <table>
2823    <title><structname>pg_index</> Columns</title>
2824
2825    <tgroup cols=4>
2826     <thead>
2827      <row>
2828       <entry>Name</entry>
2829       <entry>Type</entry>
2830       <entry>References</entry>
2831       <entry>Description</entry>
2832      </row>
2833     </thead>
2834
2835     <tbody>
2836      <row>
2837       <entry><structfield>indexrelid</structfield></entry>
2838       <entry><type>oid</type></entry>
2839       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
2840       <entry>The OID of the <structname>pg_class</> entry for this index</entry>
2841      </row>
2842
2843      <row>
2844       <entry><structfield>indrelid</structfield></entry>
2845       <entry><type>oid</type></entry>
2846       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
2847       <entry>The OID of the <structname>pg_class</> entry for the table this index is for</entry>
2848      </row>
2849
2850      <row>
2851       <entry><structfield>indnatts</structfield></entry>
2852       <entry><type>int2</type></entry>
2853       <entry></entry>
2854       <entry>The number of columns in the index (duplicates
2855       <literal>pg_class.relnatts</literal>)</entry>
2856      </row>
2857
2858      <row>
2859       <entry><structfield>indisunique</structfield></entry>
2860       <entry><type>bool</type></entry>
2861       <entry></entry>
2862       <entry>If true, this is a unique index</entry>
2863      </row>
2864
2865      <row>
2866       <entry><structfield>indisprimary</structfield></entry>
2867       <entry><type>bool</type></entry>
2868       <entry></entry>
2869       <entry>If true, this index represents the primary key of the table
2870       (<structfield>indisunique</> should always be true when this is true)</entry>
2871      </row>
2872
2873      <row>
2874       <entry><structfield>indisclustered</structfield></entry>
2875       <entry><type>bool</type></entry>
2876       <entry></entry>
2877       <entry>If true, the table was last clustered on this index</entry>
2878      </row>
2879
2880      <row>
2881       <entry><structfield>indisvalid</structfield></entry>
2882       <entry><type>bool</type></entry>
2883       <entry></entry>
2884       <entry>
2885        If true, the index is currently valid for queries.  False means the
2886        index is possibly incomplete: it must still be modified by
2887        <command>INSERT</>/<command>UPDATE</> operations, but it cannot safely
2888        be used for queries. If it is unique, the uniqueness property is not
2889        true either
2890       </entry>
2891      </row>
2892
2893      <row>
2894       <entry><structfield>indcheckxmin</structfield></entry>
2895       <entry><type>bool</type></entry>
2896       <entry></entry>
2897       <entry>
2898        If true, queries must not use the index until the <structfield>xmin</>
2899        of this <structname>pg_index</> row is below their TransactionXmin
2900        event horizon, because the table may contain broken HOT chains with
2901        incompatible rows that they can see
2902       </entry>
2903      </row>
2904
2905      <row>
2906       <entry><structfield>indisready</structfield></entry>
2907       <entry><type>bool</type></entry>
2908       <entry></entry>
2909       <entry>
2910        If true, the index is currently ready for inserts.  False means the
2911        index must be ignored by <command>INSERT</>/<command>UPDATE</>
2912        operations
2913       </entry>
2914      </row>
2915
2916      <row>
2917       <entry><structfield>indkey</structfield></entry>
2918       <entry><type>int2vector</type></entry>
2919       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</literal></entry>
2920       <entry>
2921        This is an array of <structfield>indnatts</structfield> values that
2922        indicate which table columns this index indexes.  For example a value
2923        of <literal>1 3</literal> would mean that the first and the third table
2924        columns make up the index key.  A zero in this array indicates that the
2925        corresponding index attribute is an expression over the table columns,
2926        rather than a simple column reference
2927       </entry>
2928      </row>
2929
2930      <row>
2931       <entry><structfield>indclass</structfield></entry>
2932       <entry><type>oidvector</type></entry>
2933       <entry><literal><link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link>.oid</literal></entry>
2934       <entry>
2935        For each column in the index key, this contains the OID of
2936        the operator class to use.  See
2937        <link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link> for details
2938       </entry>
2939      </row>
2940
2941      <row>
2942       <entry><structfield>indoption</structfield></entry>
2943       <entry><type>int2vector</type></entry>
2944       <entry></entry>
2945       <entry>
2946        This is an array of <structfield>indnatts</structfield> values that
2947        store per-column flag bits.  The meaning of the bits is defined by
2948        the index's access method
2949       </entry>
2950      </row>
2951
2952      <row>
2953       <entry><structfield>indexprs</structfield></entry>
2954       <entry><type>text</type></entry>
2955       <entry></entry>
2956       <entry>Expression trees (in <function>nodeToString()</function> representation)
2957       for index attributes that are not simple column references.  This is a
2958       list with one element for each zero entry in <structfield>indkey</>.
2959       NULL if all index attributes are simple references</entry>
2960      </row>
2961
2962      <row>
2963       <entry><structfield>indpred</structfield></entry>
2964       <entry><type>text</type></entry>
2965       <entry></entry>
2966       <entry>Expression tree (in <function>nodeToString()</function> representation)
2967       for partial index predicate.  NULL if not a partial index</entry>
2968      </row>
2969     </tbody>
2970    </tgroup>
2971   </table>
2972
2973  </sect1>
2974
2975
2976  <sect1 id="catalog-pg-inherits">
2977   <title><structname>pg_inherits</structname></title>
2978
2979   <indexterm zone="catalog-pg-inherits">
2980    <primary>pg_inherits</primary>
2981   </indexterm>
2982
2983   <para>
2984    The catalog <structname>pg_inherits</> records information about
2985    table inheritance hierarchies.  There is one entry for each direct
2986    child table in the database.  (Indirect inheritance can be determined
2987    by following chains of entries.)
2988   </para>
2989
2990   <table>
2991    <title><structname>pg_inherits</> Columns</title>
2992
2993    <tgroup cols=4>
2994     <thead>
2995      <row>
2996       <entry>Name</entry>
2997       <entry>Type</entry>
2998       <entry>References</entry>
2999       <entry>Description</entry>
3000      </row>
3001     </thead>
3002
3003     <tbody>
3004      <row>
3005       <entry><structfield>inhrelid</structfield></entry>
3006       <entry><type>oid</type></entry>
3007       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
3008       <entry>
3009        The OID of the child table
3010       </entry>
3011      </row>
3012
3013      <row>
3014       <entry><structfield>inhparent</structfield></entry>
3015       <entry><type>oid</type></entry>
3016       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
3017       <entry>
3018        The OID of the parent table
3019       </entry>
3020      </row>
3021
3022      <row>
3023       <entry><structfield>inhseqno</structfield></entry>
3024       <entry><type>int4</type></entry>
3025       <entry></entry>
3026       <entry>
3027        If there is more than one direct parent for a child table (multiple
3028        inheritance), this number tells the order in which the
3029        inherited columns are to be arranged.  The count starts at 1
3030       </entry>
3031      </row>
3032     </tbody>
3033    </tgroup>
3034   </table>
3035
3036  </sect1>
3037
3038
3039  <sect1 id="catalog-pg-language">
3040   <title><structname>pg_language</structname></title>
3041
3042   <indexterm zone="catalog-pg-language">
3043    <primary>pg_language</primary>
3044   </indexterm>
3045
3046   <para>
3047    The catalog <structname>pg_language</structname> registers
3048    languages in which you can write functions or stored procedures.
3049    See <xref linkend="sql-createlanguage" endterm="sql-createlanguage-title">
3050    and <xref linkend="xplang"> for more information about language handlers.
3051   </para>
3052
3053   <table>
3054    <title><structname>pg_language</> Columns</title>
3055
3056    <tgroup cols=4>
3057     <thead>
3058      <row>
3059       <entry>Name</entry>
3060       <entry>Type</entry>
3061       <entry>References</entry>
3062       <entry>Description</entry>
3063      </row>
3064     </thead>
3065
3066     <tbody>
3067      <row>
3068       <entry><structfield>lanname</structfield></entry>
3069       <entry><type>name</type></entry>
3070       <entry></entry>
3071       <entry>Name of the language</entry>
3072      </row>
3073
3074      <row>
3075       <entry><structfield>lanowner</structfield></entry>
3076       <entry><type>oid</type></entry>
3077       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
3078       <entry>Owner of the language</entry>
3079      </row>
3080
3081      <row>
3082       <entry><structfield>lanispl</structfield></entry>
3083       <entry><type>bool</type></entry>
3084       <entry></entry>
3085       <entry>
3086        This is false for internal languages (such as
3087        <acronym>SQL</acronym>) and true for user-defined languages.
3088        Currently, <application>pg_dump</application> still uses this
3089        to determine which languages need to be dumped, but this might be
3090        replaced by a different mechanism in the future
3091       </entry>
3092      </row>
3093
3094      <row>
3095       <entry><structfield>lanpltrusted</structfield></entry>
3096       <entry><type>bool</type></entry>
3097       <entry></entry>
3098       <entry>
3099        True if this is a trusted language, which means that it is believed
3100        not to grant access to anything outside the normal SQL execution
3101        environment.  Only superusers can create functions in untrusted
3102        languages
3103       </entry>
3104      </row>
3105
3106      <row>
3107       <entry><structfield>lanplcallfoid</structfield></entry>
3108       <entry><type>oid</type></entry>
3109       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
3110       <entry>
3111        For noninternal languages this references the language
3112        handler, which is a special function that is responsible for
3113        executing all functions that are written in the particular
3114        language
3115       </entry>
3116      </row>
3117
3118      <row>
3119       <entry><structfield>lanvalidator</structfield></entry>
3120       <entry><type>oid</type></entry>
3121       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
3122       <entry>
3123        This references a language validator function that is responsible
3124        for checking the syntax and validity of new functions when they
3125        are created.  Zero if no validator is provided
3126       </entry>
3127      </row>
3128
3129      <row>
3130       <entry><structfield>lanacl</structfield></entry>
3131       <entry><type>aclitem[]</type></entry>
3132       <entry></entry>
3133       <entry>
3134        Access privileges; see
3135        <xref linkend="sql-grant" endterm="sql-grant-title"> and
3136        <xref linkend="sql-revoke" endterm="sql-revoke-title">
3137        for details
3138       </entry>
3139      </row>
3140     </tbody>
3141    </tgroup>
3142   </table>
3143
3144  </sect1>
3145
3146
3147  <sect1 id="catalog-pg-largeobject">
3148   <title><structname>pg_largeobject</structname></title>
3149
3150   <indexterm zone="catalog-pg-largeobject">
3151    <primary>pg_largeobject</primary>
3152   </indexterm>
3153
3154   <para>
3155    The catalog <structname>pg_largeobject</structname> holds the data making up
3156    <quote>large objects</quote>.  A large object is identified by an
3157    OID assigned when it is created.  Each large object is broken into
3158    segments or <quote>pages</> small enough to be conveniently stored as rows
3159    in <structname>pg_largeobject</structname>.
3160    The amount of data per page is defined to be <symbol>LOBLKSIZE</> (which is currently
3161    <literal>BLCKSZ/4</>, or typically 2 kB).
3162   </para>
3163
3164   <table>
3165    <title><structname>pg_largeobject</> Columns</title>
3166
3167    <tgroup cols=3>
3168     <thead>
3169      <row>
3170       <entry>Name</entry>
3171       <entry>Type</entry>
3172       <entry>Description</entry>
3173      </row>
3174     </thead>
3175
3176     <tbody>
3177      <row>
3178       <entry><structfield>loid</structfield></entry>
3179       <entry><type>oid</type></entry>
3180       <entry>Identifier of the large object that includes this page</entry>
3181      </row>
3182
3183      <row>
3184       <entry><structfield>pageno</structfield></entry>
3185       <entry><type>int4</type></entry>
3186       <entry>Page number of this page within its large object
3187       (counting from zero)</entry>
3188      </row>
3189
3190      <row>
3191       <entry><structfield>data</structfield></entry>
3192       <entry><type>bytea</type></entry>
3193       <entry>
3194        Actual data stored in the large object.
3195        This will never be more than <symbol>LOBLKSIZE</> bytes and might be less
3196       </entry>
3197      </row>
3198     </tbody>
3199    </tgroup>
3200   </table>
3201
3202   <para>
3203    Each row of <structname>pg_largeobject</structname> holds data
3204    for one page of a large object, beginning at
3205    byte offset (<literal>pageno * LOBLKSIZE</>) within the object.  The implementation
3206    allows sparse storage: pages might be missing, and might be shorter than
3207    <literal>LOBLKSIZE</> bytes even if they are not the last page of the object.
3208    Missing regions within a large object read as zeroes.
3209   </para>
3210
3211  </sect1>
3212
3213
3214  <sect1 id="catalog-pg-listener">
3215   <title><structname>pg_listener</structname></title>
3216
3217   <indexterm zone="catalog-pg-listener">
3218    <primary>pg_listener</primary>
3219   </indexterm>
3220
3221   <para>
3222    The catalog <structname>pg_listener</structname> supports the
3223    <xref linkend="sql-listen" endterm="sql-listen-title"> and
3224    <xref linkend="sql-notify" endterm="sql-notify-title">
3225    commands.  A listener creates an entry in
3226    <structname>pg_listener</structname> for each notification name
3227    it is listening for.  A notifier scans <structname>pg_listener</structname>
3228    and updates each matching entry to show that a notification has occurred.
3229    The notifier also sends a signal (using the PID recorded in the table)
3230    to awaken the listener from sleep.
3231   </para>
3232
3233   <table>
3234    <title><structname>pg_listener</> Columns</title>
3235
3236    <tgroup cols=4>
3237     <thead>
3238      <row>
3239       <entry>Name</entry>
3240       <entry>Type</entry>
3241       <entry>References</entry>
3242       <entry>Description</entry>
3243      </row>
3244     </thead>
3245
3246     <tbody>
3247      <row>
3248       <entry><structfield>relname</structfield></entry>
3249       <entry><type>name</type></entry>
3250       <entry>
3251        Notify condition name.  (The name need not match any actual
3252        relation in the database; the name <structfield>relname</> is historical.)
3253       </entry>
3254      </row>
3255
3256      <row>
3257       <entry><structfield>listenerpid</structfield></entry>
3258       <entry><type>int4</type></entry>
3259       <entry>PID of the server process that created this entry</entry>
3260      </row>
3261
3262      <row>
3263       <entry><structfield>notification</structfield></entry>
3264       <entry><type>int4</type></entry>
3265       <entry>
3266        Zero if no event is pending for this listener.  If an event is
3267        pending, the PID of the server process that sent the notification
3268       </entry>
3269      </row>
3270     </tbody>
3271    </tgroup>
3272   </table>
3273
3274  </sect1>
3275
3276
3277  <sect1 id="catalog-pg-namespace">
3278   <title><structname>pg_namespace</structname></title>
3279
3280   <indexterm zone="catalog-pg-namespace">
3281    <primary>pg_namespace</primary>
3282   </indexterm>
3283
3284   <para>
3285    The catalog <structname>pg_namespace</> stores namespaces.
3286    A namespace is the structure underlying SQL schemas: each namespace
3287    can have a separate collection of relations, types, etc. without name
3288    conflicts.
3289   </para>
3290
3291   <table>
3292    <title><structname>pg_namespace</> Columns</title>
3293
3294    <tgroup cols=4>
3295     <thead>
3296      <row>
3297       <entry>Name</entry>
3298       <entry>Type</entry>
3299       <entry>References</entry>
3300       <entry>Description</entry>
3301      </row>
3302     </thead>
3303
3304     <tbody>
3305      <row>
3306       <entry><structfield>nspname</structfield></entry>
3307       <entry><type>name</type></entry>
3308       <entry></entry>
3309       <entry>Name of the namespace</entry>
3310      </row>
3311
3312      <row>
3313       <entry><structfield>nspowner</structfield></entry>
3314       <entry><type>oid</type></entry>
3315       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
3316       <entry>Owner of the namespace</entry>
3317      </row>
3318
3319      <row>
3320       <entry><structfield>nspacl</structfield></entry>
3321       <entry><type>aclitem[]</type></entry>
3322       <entry></entry>
3323       <entry>
3324        Access privileges; see
3325        <xref linkend="sql-grant" endterm="sql-grant-title"> and
3326        <xref linkend="sql-revoke" endterm="sql-revoke-title">
3327        for details
3328       </entry>
3329      </row>
3330     </tbody>
3331    </tgroup>
3332   </table>
3333
3334  </sect1>
3335
3336
3337  <sect1 id="catalog-pg-opclass">
3338   <title><structname>pg_opclass</structname></title>
3339
3340   <indexterm zone="catalog-pg-opclass">
3341    <primary>pg_opclass</primary>
3342   </indexterm>
3343
3344   <para>
3345    The catalog <structname>pg_opclass</structname> defines
3346    index access method operator classes.  Each operator class defines
3347    semantics for index columns of a particular data type and a particular
3348    index access method.  An operator class essentially specifies that a
3349    particular operator family is applicable to a particular indexable column
3350    data type.  The set of operators from the family that are actually usable
3351    with the indexed column are whichever ones accept the column's data type
3352    as their lefthand input.
3353   </para>
3354
3355   <para>
3356    Operator classes are described at length in <xref linkend="xindex">.
3357   </para>
3358
3359   <table>
3360    <title><structname>pg_opclass</> Columns</title>
3361
3362    <tgroup cols=4>
3363     <thead>
3364      <row>
3365       <entry>Name</entry>
3366       <entry>Type</entry>
3367       <entry>References</entry>
3368       <entry>Description</entry>
3369      </row>
3370     </thead>
3371     <tbody>
3372
3373      <row>
3374       <entry><structfield>opcmethod</structfield></entry>
3375       <entry><type>oid</type></entry>
3376       <entry><literal><link linkend="catalog-pg-am"><structname>pg_am</structname></link>.oid</literal></entry>
3377       <entry>Index access method operator class is for</entry>
3378      </row>
3379
3380      <row>
3381       <entry><structfield>opcname</structfield></entry>
3382       <entry><type>name</type></entry>
3383       <entry></entry>
3384       <entry>Name of this operator class</entry>
3385      </row>
3386
3387      <row>
3388       <entry><structfield>opcnamespace</structfield></entry>
3389       <entry><type>oid</type></entry>
3390       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
3391       <entry>Namespace of this operator class</entry>
3392      </row>
3393
3394      <row>
3395       <entry><structfield>opcowner</structfield></entry>
3396       <entry><type>oid</type></entry>
3397       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
3398       <entry>Owner of the operator class</entry>
3399      </row>
3400
3401      <row>
3402       <entry><structfield>opcfamily</structfield></entry>
3403       <entry><type>oid</type></entry>
3404       <entry><literal><link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link>.oid</literal></entry>
3405       <entry>Operator family containing the operator class</entry>
3406      </row>
3407
3408      <row>
3409       <entry><structfield>opcintype</structfield></entry>
3410       <entry><type>oid</type></entry>
3411       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3412       <entry>Data type that the operator class indexes</entry>
3413      </row>
3414
3415      <row>
3416       <entry><structfield>opcdefault</structfield></entry>
3417       <entry><type>bool</type></entry>
3418       <entry></entry>
3419       <entry>True if this operator class is the default for <structfield>opcintype</></entry>
3420      </row>
3421
3422      <row>
3423       <entry><structfield>opckeytype</structfield></entry>
3424       <entry><type>oid</type></entry>
3425       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3426       <entry>Type of data stored in index, or zero if same as <structfield>opcintype</></entry>
3427      </row>
3428
3429     </tbody>
3430    </tgroup>
3431   </table>
3432
3433   <para>
3434    An operator class's <structfield>opcmethod</> must match the
3435    <structname>opfmethod</> of its containing operator family.
3436    Also, there must be no more than one <structname>pg_opclass</structname>
3437    row having <structname>opcdefault</> true for any given combination of
3438    <structname>opcmethod</> and <structname>opcintype</>.
3439   </para>
3440
3441  </sect1>
3442
3443
3444  <sect1 id="catalog-pg-operator">
3445   <title><structname>pg_operator</structname></title>
3446
3447   <indexterm zone="catalog-pg-operator">
3448    <primary>pg_operator</primary>
3449   </indexterm>
3450
3451   <para>
3452    The catalog <structname>pg_operator</> stores information about operators.
3453    See <xref linkend="sql-createoperator" endterm="sql-createoperator-title">
3454    and <xref linkend="xoper"> for more information.
3455   </para>
3456
3457   <table>
3458    <title><structname>pg_operator</> Columns</title>
3459
3460    <tgroup cols=4>
3461     <thead>
3462      <row>
3463       <entry>Name</entry>
3464       <entry>Type</entry>
3465       <entry>References</entry>
3466       <entry>Description</entry>
3467      </row>
3468     </thead>
3469
3470     <tbody>
3471      <row>
3472       <entry><structfield>oprname</structfield></entry>
3473       <entry><type>name</type></entry>
3474       <entry></entry>
3475       <entry>Name of the operator</entry>
3476      </row>
3477
3478      <row>
3479       <entry><structfield>oprnamespace</structfield></entry>
3480       <entry><type>oid</type></entry>
3481       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
3482       <entry>
3483        The OID of the namespace that contains this operator
3484       </entry>
3485      </row>
3486
3487      <row>
3488       <entry><structfield>oprowner</structfield></entry>
3489       <entry><type>oid</type></entry>
3490       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
3491       <entry>Owner of the operator</entry>
3492      </row>
3493
3494      <row>
3495       <entry><structfield>oprkind</structfield></entry>
3496       <entry><type>char</type></entry>
3497       <entry></entry>
3498       <entry>
3499        <literal>b</> = infix (<quote>both</quote>), <literal>l</> = prefix
3500        (<quote>left</quote>), <literal>r</> = postfix (<quote>right</quote>)
3501       </entry>
3502      </row>
3503
3504      <row>
3505       <entry><structfield>oprcanmerge</structfield></entry>
3506       <entry><type>bool</type></entry>
3507       <entry></entry>
3508       <entry>This operator supports merge joins</entry>
3509      </row>
3510
3511      <row>
3512       <entry><structfield>oprcanhash</structfield></entry>
3513       <entry><type>bool</type></entry>
3514       <entry></entry>
3515       <entry>This operator supports hash joins</entry>
3516      </row>
3517
3518      <row>
3519       <entry><structfield>oprleft</structfield></entry>
3520       <entry><type>oid</type></entry>
3521       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3522       <entry>Type of the left operand</entry>
3523      </row>
3524
3525      <row>
3526       <entry><structfield>oprright</structfield></entry>
3527       <entry><type>oid</type></entry>
3528       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3529       <entry>Type of the right operand</entry>
3530      </row>
3531
3532      <row>
3533       <entry><structfield>oprresult</structfield></entry>
3534       <entry><type>oid</type></entry>
3535       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3536       <entry>Type of the result</entry>
3537      </row>
3538
3539      <row>
3540       <entry><structfield>oprcom</structfield></entry>
3541       <entry><type>oid</type></entry>
3542       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
3543       <entry>Commutator of this operator, if any</entry>
3544      </row>
3545
3546      <row>
3547       <entry><structfield>oprnegate</structfield></entry>
3548       <entry><type>oid</type></entry>
3549       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
3550       <entry>Negator of this operator, if any</entry>
3551      </row>
3552
3553      <row>
3554       <entry><structfield>oprcode</structfield></entry>
3555       <entry><type>regproc</type></entry>
3556       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
3557       <entry>Function that implements this operator</entry>
3558      </row>
3559
3560      <row>
3561       <entry><structfield>oprrest</structfield></entry>
3562       <entry><type>regproc</type></entry>
3563       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
3564       <entry>Restriction selectivity estimation function for this operator</entry>
3565      </row>
3566
3567      <row>
3568       <entry><structfield>oprjoin</structfield></entry>
3569       <entry><type>regproc</type></entry>
3570       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
3571       <entry>Join selectivity estimation function for this operator</entry>
3572      </row>
3573     </tbody>
3574    </tgroup>
3575   </table>
3576
3577   <para>
3578    Unused column contain zeroes. For example, <structfield>oprleft</structfield>
3579    is zero for a prefix operator.
3580   </para>
3581
3582  </sect1>
3583
3584
3585  <sect1 id="catalog-pg-opfamily">
3586   <title><structname>pg_opfamily</structname></title>
3587
3588   <indexterm zone="catalog-pg-opfamily">
3589    <primary>pg_opfamily</primary>
3590   </indexterm>
3591
3592   <para>
3593    The catalog <structname>pg_opfamily</structname> defines operator families.
3594    Each operator family is a collection of operators and associated
3595    support routines that implement the semantics specified for a particular
3596    index access method.  Furthermore, the operators in a family are all
3597    <quote>compatible</>, in a way that is specified by the access method.
3598    The operator family concept allows cross-data-type operators to be used
3599    with indexes and to be reasoned about using knowledge of access method
3600    semantics.
3601   </para>
3602
3603   <para>
3604    Operator families are described at length in <xref linkend="xindex">.
3605   </para>
3606
3607   <table>
3608    <title><structname>pg_opfamily</> Columns</title>
3609
3610    <tgroup cols=4>
3611     <thead>
3612      <row>
3613       <entry>Name</entry>
3614       <entry>Type</entry>
3615       <entry>References</entry>
3616       <entry>Description</entry>
3617      </row>
3618     </thead>
3619     <tbody>
3620
3621      <row>
3622       <entry><structfield>opfmethod</structfield></entry>
3623       <entry><type>oid</type></entry>
3624       <entry><literal><link linkend="catalog-pg-am"><structname>pg_am</structname></link>.oid</literal></entry>
3625       <entry>Index access method operator family is for</entry>
3626      </row>
3627
3628      <row>
3629       <entry><structfield>opfname</structfield></entry>
3630       <entry><type>name</type></entry>
3631       <entry></entry>
3632       <entry>Name of this operator family</entry>
3633      </row>
3634
3635      <row>
3636       <entry><structfield>opfnamespace</structfield></entry>
3637       <entry><type>oid</type></entry>
3638       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
3639       <entry>Namespace of this operator family</entry>
3640      </row>
3641
3642      <row>
3643       <entry><structfield>opfowner</structfield></entry>
3644       <entry><type>oid</type></entry>
3645       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
3646       <entry>Owner of the operator family</entry>
3647      </row>
3648
3649     </tbody>
3650    </tgroup>
3651   </table>
3652
3653   <para>
3654    The majority of the information defining an operator family is not in its
3655    <structname>pg_opfamily</structname> row, but in the associated rows in
3656    <link linkend="catalog-pg-amop"><structname>pg_amop</structname></link>,
3657    <link linkend="catalog-pg-amproc"><structname>pg_amproc</structname></link>,
3658    and
3659    <link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link>.
3660   </para>
3661
3662  </sect1>
3663
3664
3665  <sect1 id="catalog-pg-pltemplate">
3666   <title><structname>pg_pltemplate</structname></title>
3667
3668   <indexterm zone="catalog-pg-pltemplate">
3669    <primary>pg_pltemplate</primary>
3670   </indexterm>
3671
3672   <para>
3673    The catalog <structname>pg_pltemplate</structname> stores
3674    <quote>template</> information for procedural languages.
3675    A template for a language allows the language to be created in a
3676    particular database by a simple <command>CREATE LANGUAGE</> command,
3677    with no need to specify implementation details.
3678   </para>
3679
3680   <para>
3681    Unlike most system catalogs, <structname>pg_pltemplate</structname>
3682    is shared across all databases of a cluster: there is only one
3683    copy of <structname>pg_pltemplate</structname> per cluster, not
3684    one per database.  This allows the information to be accessible in
3685    each database as it is needed.
3686   </para>
3687
3688   <table>
3689    <title><structname>pg_pltemplate</> Columns</title>
3690
3691    <tgroup cols=3>
3692     <thead>
3693      <row>
3694       <entry>Name</entry>
3695       <entry>Type</entry>
3696       <entry>Description</entry>
3697      </row>
3698     </thead>
3699
3700     <tbody>
3701      <row>
3702       <entry><structfield>tmplname</structfield></entry>
3703       <entry><type>name</type></entry>
3704       <entry>Name of the language this template is for</entry>
3705      </row>
3706
3707      <row>
3708       <entry><structfield>tmpltrusted</structfield></entry>
3709       <entry><type>boolean</type></entry>
3710       <entry>True if language is considered trusted</entry>
3711      </row>
3712
3713      <row>
3714       <entry><structfield>tmpldbacreate</structfield></entry>
3715       <entry><type>boolean</type></entry>
3716       <entry>True if language may be created by a database owner</entry>
3717      </row>
3718
3719      <row>
3720       <entry><structfield>tmplhandler</structfield></entry>
3721       <entry><type>text</type></entry>
3722       <entry>Name of call handler function</entry>
3723      </row>
3724
3725      <row>
3726       <entry><structfield>tmplvalidator</structfield></entry>
3727       <entry><type>text</type></entry>
3728       <entry>Name of validator function, or NULL if none</entry>
3729      </row>
3730
3731      <row>
3732       <entry><structfield>tmpllibrary</structfield></entry>
3733       <entry><type>text</type></entry>
3734       <entry>Path of shared library that implements language</entry>
3735      </row>
3736
3737      <row>
3738       <entry><structfield>tmplacl</structfield></entry>
3739       <entry><type>aclitem[]</type></entry>
3740       <entry>Access privileges for template (not yet used)</entry>
3741      </row>
3742
3743     </tbody>
3744    </tgroup>
3745   </table>
3746
3747   <para>
3748    There are not currently any commands that manipulate procedural language
3749    templates; to change the built-in information, a superuser must modify
3750    the table using ordinary <command>INSERT</command>, <command>DELETE</command>,
3751    or <command>UPDATE</command> commands.  It is likely that a future
3752    release of <productname>PostgreSQL</productname> will offer
3753    commands to change the entries in a cleaner fashion.
3754   </para>
3755
3756   <para>
3757    When implemented, the <structfield>tmplacl</structfield> field will provide
3758    access control for the template itself (i.e., the right to create a
3759    language using it), not for the languages created from the template.
3760   </para>
3761
3762  </sect1>
3763
3764
3765  <sect1 id="catalog-pg-proc">
3766   <title><structname>pg_proc</structname></title>
3767
3768   <indexterm zone="catalog-pg-proc">
3769    <primary>pg_proc</primary>
3770   </indexterm>
3771
3772   <para>
3773    The catalog <structname>pg_proc</> stores information about functions (or procedures).
3774    See <xref linkend="sql-createfunction" endterm="sql-createfunction-title">
3775    and <xref linkend="xfunc"> for more information.
3776   </para>
3777
3778   <para>
3779    The table contains data for aggregate functions as well as plain functions.
3780    If <structfield>proisagg</structfield> is true, there should be a matching
3781    row in <structfield>pg_aggregate</structfield>.
3782   </para>
3783
3784   <table>
3785    <title><structname>pg_proc</> Columns</title>
3786
3787    <tgroup cols=4>
3788     <thead>
3789      <row>
3790       <entry>Name</entry>
3791       <entry>Type</entry>
3792       <entry>References</entry>
3793       <entry>Description</entry>
3794      </row>
3795     </thead>
3796
3797     <tbody>
3798      <row>
3799       <entry><structfield>proname</structfield></entry>
3800       <entry><type>name</type></entry>
3801       <entry></entry>
3802       <entry>Name of the function</entry>
3803      </row>
3804
3805      <row>
3806       <entry><structfield>pronamespace</structfield></entry>
3807       <entry><type>oid</type></entry>
3808       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
3809       <entry>
3810        The OID of the namespace that contains this function
3811       </entry>
3812      </row>
3813
3814      <row>
3815       <entry><structfield>proowner</structfield></entry>
3816       <entry><type>oid</type></entry>
3817       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
3818       <entry>Owner of the function</entry>
3819      </row>
3820
3821      <row>
3822       <entry><structfield>prolang</structfield></entry>
3823       <entry><type>oid</type></entry>
3824       <entry><literal><link linkend="catalog-pg-language"><structname>pg_language</structname></link>.oid</literal></entry>
3825       <entry>Implementation language or call interface of this function</entry>
3826      </row>
3827
3828      <row>
3829       <entry><structfield>procost</structfield></entry>
3830       <entry><type>float4</type></entry>
3831       <entry></entry>
3832       <entry>Estimated execution cost (in units of
3833        <xref linkend="guc-cpu-operator-cost">); if <structfield>proretset</>,
3834        this is cost per row returned</entry>
3835      </row>
3836
3837      <row>
3838       <entry><structfield>prorows</structfield></entry>
3839       <entry><type>float4</type></entry>
3840       <entry></entry>
3841       <entry>Estimated number of result rows (zero if not <structfield>proretset</>)</entry>
3842      </row>
3843
3844      <row>
3845       <entry><structfield>provariadic</structfield></entry>
3846       <entry><type>oid</type></entry>
3847       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3848       <entry>Data type of the variadic array parameter's elements,
3849        or zero if the function does not have a variadic parameter</entry>
3850      </row>
3851
3852      <row>
3853       <entry><structfield>proisagg</structfield></entry>
3854       <entry><type>bool</type></entry>
3855       <entry></entry>
3856       <entry>Function is an aggregate function</entry>
3857      </row>
3858
3859      <row>
3860       <entry><structfield>proiswindow</structfield></entry>
3861       <entry><type>bool</type></entry>
3862       <entry></entry>
3863       <entry>Function is a window function</entry>
3864      </row>
3865
3866      <row>
3867       <entry><structfield>prosecdef</structfield></entry>
3868       <entry><type>bool</type></entry>
3869       <entry></entry>
3870       <entry>Function is a security definer (i.e., a <quote>setuid</>
3871       function)</entry>
3872      </row>
3873
3874      <row>
3875       <entry><structfield>proisstrict</structfield></entry>
3876       <entry><type>bool</type></entry>
3877       <entry></entry>
3878       <entry>
3879        Function returns null if any call argument is null.  In that
3880        case the function won't actually be called at all.  Functions
3881        that are not <quote>strict</quote> must be prepared to handle
3882        null inputs
3883       </entry>
3884      </row>
3885
3886      <row>
3887       <entry><structfield>proretset</structfield></entry>
3888       <entry><type>bool</type></entry>
3889       <entry></entry>
3890       <entry>Function returns a set (i.e., multiple values of the specified
3891       data type)</entry>
3892      </row>
3893
3894      <row>
3895       <entry><structfield>provolatile</structfield></entry>
3896       <entry><type>char</type></entry>
3897       <entry></entry>
3898       <entry>
3899        <structfield>provolatile</structfield> tells whether the function's
3900        result depends only on its input arguments, or is affected by outside
3901        factors.
3902        It is <literal>i</literal> for <quote>immutable</> functions,
3903        which always deliver the same result for the same inputs.
3904        It is <literal>s</literal> for <quote>stable</> functions,
3905        whose results (for fixed inputs) do not change within a scan.
3906        It is <literal>v</literal> for <quote>volatile</> functions,
3907        whose results might change at any time.  (Use <literal>v</literal> also
3908        for functions with side-effects, so that calls to them cannot get
3909        optimized away.)
3910       </entry>
3911      </row>
3912
3913      <row>
3914       <entry><structfield>pronargs</structfield></entry>
3915       <entry><type>int2</type></entry>
3916       <entry></entry>
3917       <entry>Number of input arguments</entry>
3918      </row>
3919
3920      <row>
3921       <entry><structfield>pronargdefaults</structfield></entry>
3922       <entry><type>int2</type></entry>
3923       <entry></entry>
3924       <entry>Number of arguments that have defaults</entry>
3925      </row>
3926
3927      <row>
3928       <entry><structfield>prorettype</structfield></entry>
3929       <entry><type>oid</type></entry>
3930       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3931       <entry>Data type of the return value</entry>
3932      </row>
3933
3934      <row>
3935       <entry><structfield>proargtypes</structfield></entry>
3936       <entry><type>oidvector</type></entry>
3937       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3938       <entry>
3939        An array with the data types of the function arguments.  This includes
3940        only input arguments (including <literal>INOUT</literal> and
3941        <literal>VARIADIC</> arguments), and thus represents
3942        the call signature of the function
3943       </entry>
3944      </row>
3945
3946      <row>
3947       <entry><structfield>proallargtypes</structfield></entry>
3948       <entry><type>oid[]</type></entry>
3949       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3950       <entry>
3951        An array with the data types of the function arguments.  This includes
3952        all arguments (including <literal>OUT</literal> and
3953        <literal>INOUT</literal> arguments); however, if all the
3954        arguments are <literal>IN</literal> arguments, this field will be null.
3955        Note that subscripting is 1-based, whereas for historical reasons
3956        <structfield>proargtypes</> is subscripted from 0
3957       </entry>
3958      </row>
3959
3960      <row>
3961       <entry><structfield>proargmodes</structfield></entry>
3962       <entry><type>char[]</type></entry>
3963       <entry></entry>
3964       <entry>
3965         An array with the modes of the function arguments, encoded as
3966         <literal>i</literal> for <literal>IN</> arguments,
3967         <literal>o</literal> for <literal>OUT</> arguments,
3968         <literal>b</literal> for <literal>INOUT</> arguments,
3969         <literal>v</literal> for <literal>VARIADIC</> arguments,
3970         <literal>t</literal> for <literal>TABLE</> arguments.
3971         If all the arguments are <literal>IN</literal> arguments,
3972         this field will be null.
3973         Note that subscripts correspond to positions of
3974         <structfield>proallargtypes</> not <structfield>proargtypes</>
3975       </entry>
3976      </row>
3977
3978      <row>
3979       <entry><structfield>proargnames</structfield></entry>
3980       <entry><type>text[]</type></entry>
3981       <entry></entry>
3982       <entry>
3983         An array with the names of the function arguments.
3984         Arguments without a name are set to empty strings in the array.
3985         If none of the arguments have a name, this field will be null.
3986         Note that subscripts correspond to positions of
3987         <structfield>proallargtypes</> not <structfield>proargtypes</>
3988       </entry>
3989      </row>
3990
3991      <row>
3992       <entry><structfield>proargdefaults</structfield></entry>
3993       <entry><type>text</type></entry>
3994       <entry></entry>
3995       <entry>
3996        Expression trees (in <function>nodeToString()</function> representation)
3997        for default values.  This is a list with
3998        <structfield>pronargdefaults</> elements, corresponding to the last
3999        <replaceable>N</> <emphasis>input</> arguments (i.e., the last
4000        <replaceable>N</> <structfield>proargtypes</> positions).
4001        If none of the arguments have defaults, this field will be null
4002       </entry>
4003      </row>
4004
4005      <row>
4006       <entry><structfield>prosrc</structfield></entry>
4007       <entry><type>text</type></entry>
4008       <entry></entry>
4009       <entry>
4010        This tells the function handler how to invoke the function.  It
4011        might be the actual source code of the function for interpreted
4012        languages, a link symbol, a file name, or just about anything
4013        else, depending on the implementation language/call convention
4014       </entry>
4015      </row>
4016
4017      <row>
4018       <entry><structfield>probin</structfield></entry>
4019       <entry><type>bytea</type></entry>
4020       <entry></entry>
4021       <entry>
4022        Additional information about how to invoke the function.
4023        Again, the interpretation is language-specific
4024       </entry>
4025      </row>
4026
4027      <row>
4028       <entry><structfield>proconfig</structfield></entry>
4029       <entry><type>text[]</type></entry>
4030       <entry></entry>
4031       <entry>Function's local settings for run-time configuration variables</entry>
4032      </row>
4033
4034      <row>
4035       <entry><structfield>proacl</structfield></entry>
4036       <entry><type>aclitem[]</type></entry>
4037       <entry></entry>
4038       <entry>
4039        Access privileges; see
4040        <xref linkend="sql-grant" endterm="sql-grant-title"> and
4041        <xref linkend="sql-revoke" endterm="sql-revoke-title">
4042        for details
4043       </entry>
4044      </row>
4045     </tbody>
4046    </tgroup>
4047   </table>
4048
4049   <para>
4050    For compiled functions, both built-in and dynamically loaded,
4051    <structfield>prosrc</structfield> contains the function's C-language
4052    name (link symbol).  For all other currently-known language types,
4053    <structfield>prosrc</structfield> contains the function's source
4054    text.  <structfield>probin</structfield> is unused except for
4055    dynamically-loaded C functions, for which it gives the name of the
4056    shared library file containing the function.
4057   </para>
4058
4059  </sect1>
4060
4061  <sect1 id="catalog-pg-rewrite">
4062   <title><structname>pg_rewrite</structname></title>
4063
4064   <indexterm zone="catalog-pg-rewrite">
4065    <primary>pg_rewrite</primary>
4066   </indexterm>
4067
4068   <para>
4069    The catalog <structname>pg_rewrite</structname> stores rewrite rules for tables and views.
4070   </para>
4071
4072   <table>
4073    <title><structname>pg_rewrite</> Columns</title>
4074
4075    <tgroup cols=4>
4076     <thead>
4077      <row>
4078       <entry>Name</entry>
4079       <entry>Type</entry>
4080       <entry>References</entry>
4081       <entry>Description</entry>
4082      </row>
4083     </thead>
4084
4085     <tbody>
4086      <row>
4087       <entry><structfield>rulename</structfield></entry>
4088       <entry><type>name</type></entry>
4089       <entry></entry>
4090       <entry>Rule name</entry>
4091      </row>
4092
4093      <row>
4094       <entry><structfield>ev_class</structfield></entry>
4095       <entry><type>oid</type></entry>
4096       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
4097       <entry>The table this rule is for</entry>
4098      </row>
4099
4100      <row>
4101       <entry><structfield>ev_attr</structfield></entry>
4102       <entry><type>int2</type></entry>
4103       <entry></entry>
4104       <entry>The column this rule is for (currently, always zero to
4105       indicate the whole table)</entry>
4106      </row>
4107
4108      <row>
4109       <entry><structfield>ev_type</structfield></entry>
4110       <entry><type>char</type></entry>
4111       <entry></entry>
4112       <entry>
4113        Event type that the rule is for: 1 = <command>SELECT</>, 2 =
4114        <command>UPDATE</>, 3 = <command>INSERT</>, 4 =
4115        <command>DELETE</>
4116       </entry>
4117      </row>
4118
4119      <row>
4120       <entry><structfield>ev_enabled</structfield></entry>
4121       <entry><type>char</type></entry>
4122       <entry></entry>
4123       <entry>
4124        Controls in which <xref linkend="guc-session-replication-role"> modes
4125        the rule fires.
4126        <literal>O</> = rule fires in <quote>origin</> and <quote>local</> modes,
4127        <literal>D</> = rule is disabled,
4128        <literal>R</> = rule fires in <quote>replica</> mode,
4129        <literal>A</> = rule fires always.
4130       </entry>
4131      </row>
4132
4133      <row>
4134       <entry><structfield>is_instead</structfield></entry>
4135       <entry><type>bool</type></entry>
4136       <entry></entry>
4137       <entry>True if the rule is an <literal>INSTEAD</literal> rule</entry>
4138      </row>
4139
4140      <row>
4141       <entry><structfield>ev_qual</structfield></entry>
4142       <entry><type>text</type></entry>
4143       <entry></entry>
4144       <entry>
4145        Expression tree (in the form of a
4146        <function>nodeToString()</function> representation) for the
4147        rule's qualifying condition
4148       </entry>
4149      </row>
4150
4151      <row>
4152       <entry><structfield>ev_action</structfield></entry>
4153       <entry><type>text</type></entry>
4154       <entry></entry>
4155       <entry>
4156        Query tree (in the form of a
4157        <function>nodeToString()</function> representation) for the
4158        rule's action
4159       </entry>
4160      </row>
4161     </tbody>
4162    </tgroup>
4163   </table>
4164
4165   <note>
4166    <para>
4167     <literal>pg_class.relhasrules</literal>
4168     must be true if a table has any rules in this catalog.
4169    </para>
4170   </note>
4171
4172  </sect1>
4173
4174
4175  <sect1 id="catalog-pg-shdepend">
4176   <title><structname>pg_shdepend</structname></title>
4177
4178   <indexterm zone="catalog-pg-shdepend">
4179    <primary>pg_shdepend</primary>
4180   </indexterm>
4181
4182   <para>
4183    The catalog <structname>pg_shdepend</structname> records the
4184    dependency relationships between database objects and shared objects,
4185    such as roles.  This information allows
4186    <productname>PostgreSQL</productname> to ensure that those objects are
4187    unreferenced before attempting to delete them.
4188   </para>
4189
4190   <para>
4191    See also <link linkend="catalog-pg-depend"><structname>pg_depend</structname></link>,
4192    which performs a similar function for dependencies involving objects
4193    within a single database.
4194   </para>
4195
4196   <para>
4197    Unlike most system catalogs, <structname>pg_shdepend</structname>
4198    is shared across all databases of a cluster: there is only one
4199    copy of <structname>pg_shdepend</structname> per cluster, not
4200    one per database.
4201   </para>
4202
4203   <table>
4204    <title><structname>pg_shdepend</> Columns</title>
4205
4206    <tgroup cols=4>
4207     <thead>
4208      <row>
4209       <entry>Name</entry>
4210       <entry>Type</entry>
4211       <entry>References</entry>
4212       <entry>Description</entry>
4213      </row>
4214     </thead>
4215
4216     <tbody>
4217      <row>
4218       <entry><structfield>dbid</structfield></entry>
4219       <entry><type>oid</type></entry>
4220       <entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.oid</literal></entry>
4221       <entry>The OID of the database the dependent object is in,
4222        or zero for a shared object</entry>
4223      </row>
4224
4225      <row>
4226       <entry><structfield>classid</structfield></entry>
4227       <entry><type>oid</type></entry>
4228       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
4229       <entry>The OID of the system catalog the dependent object is in</entry>
4230      </row>
4231
4232      <row>
4233       <entry><structfield>objid</structfield></entry>
4234       <entry><type>oid</type></entry>
4235       <entry>any OID column</entry>
4236       <entry>The OID of the specific dependent object</entry>
4237      </row>
4238
4239      <row>
4240       <entry><structfield>refclassid</structfield></entry>
4241       <entry><type>oid</type></entry>
4242       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
4243       <entry>The OID of the system catalog the referenced object is in
4244        (must be a shared catalog)</entry>
4245      </row>
4246
4247      <row>
4248       <entry><structfield>refobjid</structfield></entry>
4249       <entry><type>oid</type></entry>
4250       <entry>any OID column</entry>
4251       <entry>The OID of the specific referenced object</entry>
4252      </row>
4253
4254      <row>
4255       <entry><structfield>deptype</structfield></entry>
4256       <entry><type>char</type></entry>
4257       <entry></entry>
4258       <entry>
4259        A code defining the specific semantics of this dependency relationship; see text
4260       </entry>
4261      </row>
4262
4263     </tbody>
4264    </tgroup>
4265   </table>
4266
4267   <para>
4268    In all cases, a <structname>pg_shdepend</structname> entry indicates that
4269    the referenced object cannot be dropped without also dropping the dependent
4270    object.  However, there are several subflavors identified by
4271    <structfield>deptype</>:
4272
4273    <variablelist>
4274     <varlistentry>
4275      <term><symbol>SHARED_DEPENDENCY_OWNER</> (<literal>o</>)</term>
4276      <listitem>
4277       <para>
4278        The referenced object (which must be a role) is the owner of the
4279        dependent object.
4280       </para>
4281      </listitem>
4282     </varlistentry>
4283
4284     <varlistentry>
4285      <term><symbol>SHARED_DEPENDENCY_ACL</> (<literal>a</>)</term>
4286      <listitem>
4287       <para>
4288        The referenced object (which must be a role) is mentioned in the
4289        ACL (access control list, i.e., privileges list) of the
4290        dependent object.  (A <symbol>SHARED_DEPENDENCY_ACL</> entry is
4291        not made for the owner of the object, since the owner will have
4292        a <symbol>SHARED_DEPENDENCY_OWNER</> entry anyway.)
4293       </para>
4294      </listitem>
4295     </varlistentry>
4296
4297     <varlistentry>
4298      <term><symbol>SHARED_DEPENDENCY_PIN</> (<literal>p</>)</term>
4299      <listitem>
4300       <para>
4301        There is no dependent object; this type of entry is a signal
4302        that the system itself depends on the referenced object, and so
4303        that object must never be deleted.  Entries of this type are
4304        created only by <command>initdb</command>.  The columns for the
4305        dependent object contain zeroes.
4306       </para>
4307      </listitem>
4308     </varlistentry>
4309    </variablelist>
4310
4311    Other dependency flavors might be needed in future.  Note in particular
4312    that the current definition only supports roles as referenced objects.
4313   </para>
4314
4315  </sect1>
4316
4317  <sect1 id="catalog-pg-shdescription">
4318   <title><structname>pg_shdescription</structname></title>
4319
4320   <indexterm zone="catalog-pg-shdescription">
4321    <primary>pg_shdescription</primary>
4322   </indexterm>
4323
4324   <para>
4325    The catalog <structname>pg_shdescription</structname> stores optional
4326    descriptions (comments) for shared database objects.  Descriptions can be
4327    manipulated with the <xref linkend="sql-comment"
4328    endterm="sql-comment-title"> command and viewed with
4329    <application>psql</application>'s <literal>\d</literal> commands.
4330   </para>
4331
4332   <para>
4333    See also <link linkend="catalog-pg-description"><structname>pg_description</structname></link>,
4334    which performs a similar function for descriptions involving objects
4335    within a single database.
4336   </para>
4337
4338   <para>
4339    Unlike most system catalogs, <structname>pg_shdescription</structname>
4340    is shared across all databases of a cluster: there is only one
4341    copy of <structname>pg_shdescription</structname> per cluster, not
4342    one per database.
4343   </para>
4344
4345   <table>
4346    <title><structname>pg_shdescription</> Columns</title>
4347
4348    <tgroup cols=4>
4349     <thead>
4350      <row>
4351       <entry>Name</entry>
4352       <entry>Type</entry>
4353       <entry>References</entry>
4354       <entry>Description</entry>
4355      </row>
4356     </thead>
4357
4358     <tbody>
4359      <row>
4360       <entry><structfield>objoid</structfield></entry>
4361       <entry><type>oid</type></entry>
4362       <entry>any OID column</entry>
4363       <entry>The OID of the object this description pertains to</entry>
4364      </row>
4365
4366      <row>
4367       <entry><structfield>classoid</structfield></entry>
4368       <entry><type>oid</type></entry>
4369       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
4370       <entry>The OID of the system catalog this object appears in</entry>
4371      </row>
4372
4373      <row>
4374       <entry><structfield>description</structfield></entry>
4375       <entry><type>text</type></entry>
4376       <entry></entry>
4377       <entry>Arbitrary text that serves as the description of this object</entry>
4378      </row>
4379     </tbody>
4380    </tgroup>
4381   </table>
4382
4383  </sect1>
4384
4385
4386  <sect1 id="catalog-pg-statistic">
4387   <title><structname>pg_statistic</structname></title>
4388
4389   <indexterm zone="catalog-pg-statistic">
4390    <primary>pg_statistic</primary>
4391   </indexterm>
4392
4393   <para>
4394    The catalog <structname>pg_statistic</structname> stores
4395    statistical data about the contents of the database.  Entries are
4396    created by <xref linkend="sql-analyze" endterm="sql-analyze-title">
4397    and subsequently used by the query planner.  There is one entry for
4398    each table column that has been analyzed.  Note that all the
4399    statistical data is inherently approximate, even assuming that it
4400    is up-to-date.
4401   </para>
4402
4403   <para>
4404    <structname>pg_statistic</structname> also stores statistical data about
4405    the values of index expressions.  These are described as if they were
4406    actual data columns; in particular, <structfield>starelid</structfield>
4407    references the index.  No entry is made for an ordinary non-expression
4408    index column, however, since it would be redundant with the entry
4409    for the underlying table column.
4410   </para>
4411
4412   <para>
4413    Since different kinds of statistics might be appropriate for different
4414    kinds of data, <structname>pg_statistic</structname> is designed not
4415    to assume very much about what sort of statistics it stores.  Only
4416    extremely general statistics (such as nullness) are given dedicated
4417    columns in <structname>pg_statistic</structname>.  Everything else
4418    is stored in <quote>slots</quote>, which are groups of associated columns
4419    whose content is identified by a code number in one of the slot's columns.
4420    For more information see
4421    <filename>src/include/catalog/pg_statistic.h</filename>.
4422   </para>
4423
4424   <para>
4425    <structname>pg_statistic</structname> should not be readable by the
4426    public, since even statistical information about a table's contents
4427    might be considered sensitive.  (Example: minimum and maximum values
4428    of a salary column might be quite interesting.)
4429    <link linkend="view-pg-stats"><structname>pg_stats</structname></link>
4430    is a publicly readable view on
4431    <structname>pg_statistic</structname> that only exposes information
4432    about those tables that are readable by the current user.
4433   </para>
4434
4435   <table>
4436    <title><structname>pg_statistic</> Columns</title>
4437
4438    <tgroup cols=4>
4439     <thead>
4440      <row>
4441       <entry>Name</entry>
4442       <entry>Type</entry>
4443       <entry>References</entry>
4444       <entry>Description</entry>
4445      </row>
4446     </thead>
4447
4448     <tbody>
4449      <row>
4450       <entry><structfield>starelid</structfield></entry>
4451       <entry><type>oid</type></entry>
4452       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
4453       <entry>The table or index that the described column belongs to</entry>
4454      </row>
4455
4456      <row>
4457       <entry><structfield>staattnum</structfield></entry>
4458       <entry><type>int2</type></entry>
4459       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</literal></entry>
4460       <entry>The number of the described column</entry>
4461      </row>
4462
4463      <row>
4464       <entry><structfield>stanullfrac</structfield></entry>
4465       <entry><type>float4</type></entry>
4466       <entry></entry>
4467       <entry>The fraction of the column's entries that are null</entry>
4468      </row>
4469
4470      <row>
4471       <entry><structfield>stawidth</structfield></entry>
4472       <entry><type>int4</type></entry>
4473       <entry></entry>
4474       <entry>The average stored width, in bytes, of nonnull entries</entry>
4475      </row>
4476
4477      <row>
4478       <entry><structfield>stadistinct</structfield></entry>
4479       <entry><type>float4</type></entry>
4480       <entry></entry>
4481       <entry>The number of distinct nonnull data values in the column.
4482       A value greater than zero is the actual number of distinct values.
4483       A value less than zero is the negative of a fraction of the number
4484       of rows in the table (for example, a column in which values appear about
4485       twice on the average could be represented by <structfield>stadistinct</> = -0.5).
4486       A zero value means the number of distinct values is unknown
4487       </entry>
4488      </row>
4489
4490      <row>
4491       <entry><structfield>stakind<replaceable>N</></structfield></entry>
4492       <entry><type>int2</type></entry>
4493       <entry></entry>
4494       <entry>
4495        A code number indicating the kind of statistics stored in the
4496        <replaceable>N</>th <quote>slot</quote> of the
4497        <structname>pg_statistic</structname> row
4498       </entry>
4499      </row>
4500
4501      <row>
4502       <entry><structfield>staop<replaceable>N</></structfield></entry>
4503       <entry><type>oid</type></entry>
4504       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
4505       <entry>
4506        An operator used to derive the statistics stored in the
4507        <replaceable>N</>th <quote>slot</quote>.  For example, a
4508        histogram slot would show the <literal>&lt;</literal> operator
4509        that defines the sort order of the data
4510       </entry>
4511      </row>
4512
4513      <row>
4514       <entry><structfield>stanumbers<replaceable>N</></structfield></entry>
4515       <entry><type>float4[]</type></entry>
4516       <entry></entry>
4517       <entry>
4518        Numerical statistics of the appropriate kind for the
4519        <replaceable>N</>th <quote>slot</quote>, or NULL if the slot
4520        kind does not involve numerical values
4521       </entry>
4522      </row>
4523
4524      <row>
4525       <entry><structfield>stavalues<replaceable>N</></structfield></entry>
4526       <entry><type>anyarray</type></entry>
4527       <entry></entry>
4528       <entry>
4529        Column data values of the appropriate kind for the
4530        <replaceable>N</>th <quote>slot</quote>, or NULL if the slot
4531        kind does not store any data values.  Each array's element
4532        values are actually of the specific column's data type, so there
4533        is no way to define these columns' type more specifically than
4534        <type>anyarray</>
4535       </entry>
4536      </row>
4537     </tbody>
4538    </tgroup>
4539   </table>
4540
4541  </sect1>
4542
4543
4544  <sect1 id="catalog-pg-tablespace">
4545   <title><structname>pg_tablespace</structname></title>
4546
4547   <indexterm zone="catalog-pg-tablespace">
4548    <primary>pg_tablespace</primary>
4549   </indexterm>
4550
4551   <para>
4552    The catalog <structname>pg_tablespace</structname> stores information
4553    about the available tablespaces.  Tables can be placed in particular
4554    tablespaces to aid administration of disk layout.
4555   </para>
4556
4557   <para>
4558    Unlike most system catalogs, <structname>pg_tablespace</structname>
4559    is shared across all databases of a cluster: there is only one
4560    copy of <structname>pg_tablespace</structname> per cluster, not
4561    one per database.
4562   </para>
4563
4564   <table>
4565    <title><structname>pg_tablespace</> Columns</title>
4566
4567    <tgroup cols=4>
4568     <thead>
4569      <row>
4570       <entry>Name</entry>
4571       <entry>Type</entry>
4572       <entry>References</entry>
4573       <entry>Description</entry>
4574      </row>
4575     </thead>
4576
4577     <tbody>
4578      <row>
4579       <entry><structfield>spcname</structfield></entry>
4580       <entry><type>name</type></entry>
4581       <entry></entry>
4582       <entry>Tablespace name</entry>
4583      </row>
4584
4585      <row>
4586       <entry><structfield>spcowner</structfield></entry>
4587       <entry><type>oid</type></entry>
4588       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
4589       <entry>Owner of the tablespace, usually the user who created it</entry>
4590      </row>
4591
4592      <row>
4593       <entry><structfield>spclocation</structfield></entry>
4594       <entry><type>text</type></entry>
4595       <entry></entry>
4596       <entry>Location (directory path) of the tablespace</entry>
4597      </row>
4598
4599      <row>
4600       <entry><structfield>spcacl</structfield></entry>
4601       <entry><type>aclitem[]</type></entry>
4602       <entry></entry>
4603       <entry>
4604        Access privileges; see
4605        <xref linkend="sql-grant" endterm="sql-grant-title"> and
4606        <xref linkend="sql-revoke" endterm="sql-revoke-title">
4607        for details
4608       </entry>
4609      </row>
4610     </tbody>
4611    </tgroup>
4612   </table>
4613  </sect1>
4614
4615
4616  <sect1 id="catalog-pg-trigger">
4617   <title><structname>pg_trigger</structname></title>
4618
4619   <indexterm zone="catalog-pg-trigger">
4620    <primary>pg_trigger</primary>
4621   </indexterm>
4622
4623   <para>
4624    The catalog <structname>pg_trigger</structname> stores triggers on tables.
4625    See <xref linkend="sql-createtrigger" endterm="sql-createtrigger-title">
4626    for more information.
4627   </para>
4628
4629   <table>
4630    <title><structname>pg_trigger</> Columns</title>
4631
4632    <tgroup cols=4>
4633     <thead>
4634      <row>
4635       <entry>Name</entry>
4636       <entry>Type</entry>
4637       <entry>References</entry>
4638       <entry>Description</entry>
4639      </row>
4640     </thead>
4641
4642     <tbody>
4643      <row>
4644       <entry><structfield>tgrelid</structfield></entry>
4645       <entry><type>oid</type></entry>
4646       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
4647       <entry>The table this trigger is on</entry>
4648      </row>
4649
4650      <row>
4651       <entry><structfield>tgname</structfield></entry>
4652       <entry><type>name</type></entry>
4653       <entry></entry>
4654       <entry>Trigger name (must be unique among triggers of same table)</entry>
4655      </row>
4656
4657      <row>
4658       <entry><structfield>tgfoid</structfield></entry>
4659       <entry><type>oid</type></entry>
4660       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
4661       <entry>The function to be called</entry>
4662      </row>
4663
4664      <row>
4665       <entry><structfield>tgtype</structfield></entry>
4666       <entry><type>int2</type></entry>
4667       <entry></entry>
4668       <entry>Bit mask identifying trigger conditions</entry>
4669      </row>
4670
4671      <row>
4672       <entry><structfield>tgenabled</structfield></entry>
4673       <entry><type>char</type></entry>
4674       <entry></entry>
4675       <entry>
4676        Controls in which <xref linkend="guc-session-replication-role"> modes
4677        the trigger fires.
4678        <literal>O</> = trigger fires in <quote>origin</> and <quote>local</> modes,
4679        <literal>D</> = trigger is disabled,
4680        <literal>R</> = trigger fires in <quote>replica</> mode,
4681        <literal>A</> = trigger fires always.
4682       </entry>
4683      </row>
4684
4685      <row>
4686       <entry><structfield>tgisconstraint</structfield></entry>
4687       <entry><type>bool</type></entry>
4688       <entry></entry>
4689       <entry>True if trigger is a <quote>constraint trigger</></entry>
4690      </row>
4691
4692      <row>
4693       <entry><structfield>tgconstrname</structfield></entry>
4694       <entry><type>name</type></entry>
4695       <entry></entry>
4696       <entry>Constraint name, if a constraint trigger</entry>
4697      </row>
4698
4699      <row>
4700       <entry><structfield>tgconstrrelid</structfield></entry>
4701       <entry><type>oid</type></entry>
4702       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
4703       <entry>The table referenced by a referential integrity constraint</entry>
4704      </row>
4705
4706      <row>
4707       <entry><structfield>tgconstraint</structfield></entry>
4708       <entry><type>oid</type></entry>
4709       <entry><literal><link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link>.oid</literal></entry>
4710       <entry>The <structname>pg_constraint</> entry owning the trigger, if any</entry>
4711      </row>
4712
4713      <row>
4714       <entry><structfield>tgdeferrable</structfield></entry>
4715       <entry><type>bool</type></entry>
4716       <entry></entry>
4717       <entry>True if constraint trigger is deferrable</entry>
4718      </row>
4719
4720      <row>
4721       <entry><structfield>tginitdeferred</structfield></entry>
4722       <entry><type>bool</type></entry>
4723       <entry></entry>
4724       <entry>True if constraint trigger is initially deferred</entry>
4725      </row>
4726
4727      <row>
4728       <entry><structfield>tgnargs</structfield></entry>
4729       <entry><type>int2</type></entry>
4730       <entry></entry>
4731       <entry>Number of argument strings passed to trigger function</entry>
4732      </row>
4733
4734      <row>
4735       <entry><structfield>tgattr</structfield></entry>
4736       <entry><type>int2vector</type></entry>
4737       <entry></entry>
4738       <entry>Currently unused</entry>
4739      </row>
4740
4741      <row>
4742       <entry><structfield>tgargs</structfield></entry>
4743       <entry><type>bytea</type></entry>
4744       <entry></entry>
4745       <entry>Argument strings to pass to trigger, each NULL-terminated</entry>
4746      </row>
4747     </tbody>
4748    </tgroup>
4749   </table>
4750
4751   <note>
4752    <para>
4753     When <structfield>tgconstraint</> is nonzero,
4754     <structfield>tgisconstraint</> must be true, and
4755     <structfield>tgconstrname</>, <structfield>tgconstrrelid</>,
4756     <structfield>tgdeferrable</>, <structfield>tginitdeferred</> are redundant
4757     with the referenced <structname>pg_constraint</> entry.  The reason we
4758     keep these fields is that we support <quote>stand-alone</> constraint
4759     triggers with no corresponding <structname>pg_constraint</> entry.
4760    </para>
4761   </note>
4762
4763   <note>
4764    <para>
4765     <literal>pg_class.relhastriggers</literal>
4766     must be true if a table has any triggers in this catalog.
4767    </para>
4768   </note>
4769
4770  </sect1>
4771
4772
4773  <sect1 id="catalog-pg-ts-config">
4774   <title><structname>pg_ts_config</structname></title>
4775
4776   <indexterm zone="catalog-pg-ts-config">
4777    <primary>pg_ts_config</primary>
4778   </indexterm>
4779
4780   <para>
4781    The <structname>pg_ts_config</structname> catalog contains entries
4782    representing text search configurations.  A configuration specifies
4783    a particular text search parser and a list of dictionaries to use
4784    for each of the parser's output token types.  The parser is shown
4785    in the <structname>pg_ts_config</structname> entry, but the
4786    token-to-dictionary mapping is defined by subsidiary entries in <link
4787    linkend="catalog-pg-ts-config-map"><structname>pg_ts_config_map</structname></link>.
4788   </para>
4789
4790   <para>
4791    <productname>PostgreSQL</productname>'s text search features are
4792    described at length in <xref linkend="textsearch">.
4793   </para>
4794
4795   <table>
4796    <title><structname>pg_ts_config</> Columns</title>
4797
4798    <tgroup cols=4>
4799     <thead>
4800      <row>
4801       <entry>Name</entry>
4802       <entry>Type</entry>
4803       <entry>References</entry>
4804       <entry>Description</entry>
4805      </row>
4806     </thead>
4807
4808     <tbody>
4809      <row>
4810       <entry><structfield>cfgname</structfield></entry>
4811       <entry><type>name</type></entry>
4812       <entry></entry>
4813       <entry>Text search configuration name</entry>
4814      </row>
4815
4816      <row>
4817       <entry><structfield>cfgnamespace</structfield></entry>
4818       <entry><type>oid</type></entry>
4819       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
4820       <entry>
4821        The OID of the namespace that contains this configuration
4822       </entry>
4823      </row>
4824
4825      <row>
4826       <entry><structfield>cfgowner</structfield></entry>
4827       <entry><type>oid</type></entry>
4828       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
4829       <entry>Owner of the configuration</entry>
4830      </row>
4831
4832      <row>
4833       <entry><structfield>cfgparser</structfield></entry>
4834       <entry><type>oid</type></entry>
4835       <entry><literal><link linkend="catalog-pg-ts-parser"><structname>pg_ts_parser</structname></link>.oid</literal></entry>
4836       <entry>The OID of the text search parser for this configuration</entry>
4837      </row>
4838     </tbody>
4839    </tgroup>
4840   </table>
4841  </sect1>
4842
4843
4844  <sect1 id="catalog-pg-ts-config-map">
4845   <title><structname>pg_ts_config_map</structname></title>
4846
4847   <indexterm zone="catalog-pg-ts-config-map">
4848    <primary>pg_ts_config_map</primary>
4849   </indexterm>
4850
4851   <para>
4852    The <structname>pg_ts_config_map</structname> catalog contains entries
4853    showing which text search dictionaries should be consulted, and in
4854    what order, for each output token type of each text search configuration's
4855    parser.
4856   </para>
4857
4858   <para>
4859    <productname>PostgreSQL</productname>'s text search features are
4860    described at length in <xref linkend="textsearch">.
4861   </para>
4862
4863   <table>
4864    <title><structname>pg_ts_config_map</> Columns</title>
4865
4866    <tgroup cols=4>
4867     <thead>
4868      <row>
4869       <entry>Name</entry>
4870       <entry>Type</entry>
4871       <entry>References</entry>
4872       <entry>Description</entry>
4873      </row>
4874     </thead>
4875
4876     <tbody>
4877      <row>
4878       <entry><structfield>mapcfg</structfield></entry>
4879       <entry><type>oid</type></entry>
4880       <entry><literal><link linkend="catalog-pg-ts-config"><structname>pg_ts_config</structname></link>.oid</literal></entry>
4881       <entry>The OID of the <structname>pg_ts_config</> entry owning this map entry</entry>
4882      </row>
4883
4884      <row>
4885       <entry><structfield>maptokentype</structfield></entry>
4886       <entry><type>integer</type></entry>
4887       <entry></entry>
4888       <entry>A token type emitted by the configuration's parser</entry>
4889      </row>
4890
4891      <row>
4892       <entry><structfield>mapseqno</structfield></entry>
4893       <entry><type>integer</type></entry>
4894       <entry></entry>
4895       <entry>Order in which to consult this entry (lower
4896        <structfield>mapseqno</>s first)</entry>
4897      </row>
4898
4899      <row>
4900       <entry><structfield>mapdict</structfield></entry>
4901       <entry><type>oid</type></entry>
4902       <entry><literal><link linkend="catalog-pg-ts-dict"><structname>pg_ts_dict</structname></link>.oid</literal></entry>
4903       <entry>The OID of the text search dictionary to consult</entry>
4904      </row>
4905     </tbody>
4906    </tgroup>
4907   </table>
4908  </sect1>
4909
4910
4911  <sect1 id="catalog-pg-ts-dict">
4912   <title><structname>pg_ts_dict</structname></title>
4913
4914   <indexterm zone="catalog-pg-ts-dict">
4915    <primary>pg_ts_dict</primary>
4916   </indexterm>
4917
4918   <para>
4919    The <structname>pg_ts_dict</structname> catalog contains entries
4920    defining text search dictionaries.  A dictionary depends on a text
4921    search template, which specifies all the implementation functions
4922    needed; the dictionary itself provides values for the user-settable
4923    parameters supported by the template.  This division of labor allows
4924    dictionaries to be created by unprivileged users.  The parameters
4925    are specified by a text string <structfield>dictinitoption</>,
4926    whose format and meaning vary depending on the template.
4927   </para>
4928
4929   <para>
4930    <productname>PostgreSQL</productname>'s text search features are
4931    described at length in <xref linkend="textsearch">.
4932   </para>
4933
4934   <table>
4935    <title><structname>pg_ts_dict</> Columns</title>
4936
4937    <tgroup cols=4>
4938     <thead>
4939      <row>
4940       <entry>Name</entry>
4941       <entry>Type</entry>
4942       <entry>References</entry>
4943       <entry>Description</entry>
4944      </row>
4945     </thead>
4946
4947     <tbody>
4948      <row>
4949       <entry><structfield>dictname</structfield></entry>
4950       <entry><type>name</type></entry>
4951       <entry></entry>
4952       <entry>Text search dictionary name</entry>
4953      </row>
4954
4955      <row>
4956       <entry><structfield>dictnamespace</structfield></entry>
4957       <entry><type>oid</type></entry>
4958       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
4959       <entry>
4960        The OID of the namespace that contains this dictionary
4961       </entry>
4962      </row>
4963
4964      <row>
4965       <entry><structfield>dictowner</structfield></entry>
4966       <entry><type>oid</type></entry>
4967       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
4968       <entry>Owner of the dictionary</entry>
4969      </row>
4970
4971      <row>
4972       <entry><structfield>dicttemplate</structfield></entry>
4973       <entry><type>oid</type></entry>
4974       <entry><literal><link linkend="catalog-pg-ts-template"><structname>pg_ts_template</structname></link>.oid</literal></entry>
4975       <entry>The OID of the text search template for this dictionary</entry>
4976      </row>
4977
4978      <row>
4979       <entry><structfield>dictinitoption</structfield></entry>
4980       <entry><type>text</type></entry>
4981       <entry></entry>
4982       <entry>Initialization option string for the template</entry>
4983      </row>
4984     </tbody>
4985    </tgroup>
4986   </table>
4987  </sect1>
4988
4989
4990  <sect1 id="catalog-pg-ts-parser">
4991   <title><structname>pg_ts_parser</structname></title>
4992
4993   <indexterm zone="catalog-pg-ts-parser">
4994    <primary>pg_ts_parser</primary>
4995   </indexterm>
4996
4997   <para>
4998    The <structname>pg_ts_parser</structname> catalog contains entries
4999    defining text search parsers.  A parser is responsible for splitting
5000    input text into lexemes and assigning a token type to each lexeme.
5001    Since a parser must be implemented by C-language-level functions,
5002    creation of new parsers is restricted to database superusers.
5003   </para>
5004
5005   <para>
5006    <productname>PostgreSQL</productname>'s text search features are
5007    described at length in <xref linkend="textsearch">.
5008   </para>
5009
5010   <table>
5011    <title><structname>pg_ts_parser</> Columns</title>
5012
5013    <tgroup cols=4>
5014     <thead>
5015      <row>
5016       <entry>Name</entry>
5017       <entry>Type</entry>
5018       <entry>References</entry>
5019       <entry>Description</entry>
5020      </row>
5021     </thead>
5022
5023     <tbody>
5024      <row>
5025       <entry><structfield>prsname</structfield></entry>
5026       <entry><type>name</type></entry>
5027       <entry></entry>
5028       <entry>Text search parser name</entry>
5029      </row>
5030
5031      <row>
5032       <entry><structfield>prsnamespace</structfield></entry>
5033       <entry><type>oid</type></entry>
5034       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
5035       <entry>
5036        The OID of the namespace that contains this parser
5037       </entry>
5038      </row>
5039
5040      <row>
5041       <entry><structfield>prsstart</structfield></entry>
5042       <entry><type>regproc</type></entry>
5043       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5044       <entry>OID of the parser's startup function</entry>
5045      </row>
5046
5047      <row>
5048       <entry><structfield>prstoken</structfield></entry>
5049       <entry><type>regproc</type></entry>
5050       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5051       <entry>OID of the parser's next-token function</entry>
5052      </row>
5053
5054      <row>
5055       <entry><structfield>prsend</structfield></entry>
5056       <entry><type>regproc</type></entry>
5057       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5058       <entry>OID of the parser's shutdown function</entry>
5059      </row>
5060
5061      <row>
5062       <entry><structfield>prsheadline</structfield></entry>
5063       <entry><type>regproc</type></entry>
5064       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5065       <entry>OID of the parser's headline function</entry>
5066      </row>
5067
5068      <row>
5069       <entry><structfield>prslextype</structfield></entry>
5070       <entry><type>regproc</type></entry>
5071       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5072       <entry>OID of the parser's lextype function</entry>
5073      </row>
5074     </tbody>
5075    </tgroup>
5076   </table>
5077  </sect1>
5078
5079
5080  <sect1 id="catalog-pg-ts-template">
5081   <title><structname>pg_ts_template</structname></title>
5082
5083   <indexterm zone="catalog-pg-ts-template">
5084    <primary>pg_ts_template</primary>
5085   </indexterm>
5086
5087   <para>
5088    The <structname>pg_ts_template</structname> catalog contains entries
5089    defining text search templates.  A template is the implementation
5090    skeleton for a class of text search dictionaries.
5091    Since a template must be implemented by C-language-level functions,
5092    creation of new templates is restricted to database superusers.
5093   </para>
5094
5095   <para>
5096    <productname>PostgreSQL</productname>'s text search features are
5097    described at length in <xref linkend="textsearch">.
5098   </para>
5099
5100   <table>
5101    <title><structname>pg_ts_template</> Columns</title>
5102
5103    <tgroup cols=4>
5104     <thead>
5105      <row>
5106       <entry>Name</entry>
5107       <entry>Type</entry>
5108       <entry>References</entry>
5109       <entry>Description</entry>
5110      </row>
5111     </thead>
5112
5113     <tbody>
5114      <row>
5115       <entry><structfield>tmplname</structfield></entry>
5116       <entry><type>name</type></entry>
5117       <entry></entry>
5118       <entry>Text search template name</entry>
5119      </row>
5120
5121      <row>
5122       <entry><structfield>tmplnamespace</structfield></entry>
5123       <entry><type>oid</type></entry>
5124       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
5125       <entry>
5126        The OID of the namespace that contains this template
5127       </entry>
5128      </row>
5129
5130      <row>
5131       <entry><structfield>tmplinit</structfield></entry>
5132       <entry><type>regproc</type></entry>
5133       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5134       <entry>OID of the template's initialization function</entry>
5135      </row>
5136
5137      <row>
5138       <entry><structfield>tmpllexize</structfield></entry>
5139       <entry><type>regproc</type></entry>
5140       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5141       <entry>OID of the template's lexize function</entry>
5142      </row>
5143     </tbody>
5144    </tgroup>
5145   </table>
5146  </sect1>
5147
5148
5149  <sect1 id="catalog-pg-type">
5150   <title><structname>pg_type</structname></title>
5151
5152   <indexterm zone="catalog-pg-type">
5153    <primary>pg_type</primary>
5154   </indexterm>
5155
5156   <para>
5157    The catalog <structname>pg_type</structname> stores information about data
5158    types.  Base types and enum types (scalar types) are created with
5159    <xref linkend="sql-createtype" endterm="sql-createtype-title">, and
5160    domains with
5161    <xref linkend="sql-createdomain" endterm="sql-createdomain-title">.
5162    A composite type is automatically created for each table in the database, to
5163    represent the row structure of the table.  It is also possible to create
5164    composite types with <command>CREATE TYPE AS</command>.
5165   </para>
5166
5167   <table>
5168    <title><structname>pg_type</> Columns</title>
5169
5170    <tgroup cols=4>
5171     <thead>
5172      <row>
5173       <entry>Name</entry>
5174       <entry>Type</entry>
5175       <entry>References</entry>
5176       <entry>Description</entry>
5177      </row>
5178     </thead>
5179
5180     <tbody>
5181      <row>
5182       <entry><structfield>typname</structfield></entry>
5183       <entry><type>name</type></entry>
5184       <entry></entry>
5185       <entry>Data type name</entry>
5186      </row>
5187
5188      <row>
5189       <entry><structfield>typnamespace</structfield></entry>
5190       <entry><type>oid</type></entry>
5191       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
5192       <entry>
5193        The OID of the namespace that contains this type
5194       </entry>
5195      </row>
5196
5197      <row>
5198       <entry><structfield>typowner</structfield></entry>
5199       <entry><type>oid</type></entry>
5200       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
5201       <entry>Owner of the type</entry>
5202      </row>
5203
5204      <row>
5205       <entry><structfield>typlen</structfield></entry>
5206       <entry><type>int2</type></entry>
5207       <entry></entry>
5208       <entry>
5209        For a fixed-size type, <structfield>typlen</structfield> is the number
5210        of bytes in the internal representation of the type.  But for a
5211        variable-length type, <structfield>typlen</structfield> is negative.
5212        -1 indicates a <quote>varlena</> type (one that has a length word),
5213        -2 indicates a null-terminated C string.
5214       </entry>
5215      </row>
5216
5217      <row>
5218       <entry><structfield>typbyval</structfield></entry>
5219       <entry><type>bool</type></entry>
5220       <entry></entry>
5221       <entry>
5222        <structfield>typbyval</structfield> determines whether internal
5223        routines pass a value of this type by value or by reference.
5224        <structfield>typbyval</structfield> had better be false if
5225        <structfield>typlen</structfield> is not 1, 2, or 4 (or 8 on machines
5226        where Datum is 8 bytes).
5227        Variable-length types are always passed by reference. Note that
5228        <structfield>typbyval</structfield> can be false even if the
5229        length would allow pass-by-value
5230       </entry>
5231      </row>
5232
5233      <row>
5234       <entry><structfield>typtype</structfield></entry>
5235       <entry><type>char</type></entry>
5236       <entry></entry>
5237       <entry>
5238        <structfield>typtype</structfield> is
5239        <literal>b</literal> for a base type,
5240        <literal>c</literal> for a composite type (e.g., a table's row type),
5241        <literal>d</literal> for a domain,
5242        <literal>e</literal> for an enum type,
5243        or <literal>p</literal> for a pseudo-type.
5244        See also <structfield>typrelid</structfield> and
5245        <structfield>typbasetype</structfield>
5246       </entry>
5247      </row>
5248
5249      <row>
5250       <entry><structfield>typcategory</structfield></entry>
5251       <entry><type>char</type></entry>
5252       <entry></entry>
5253       <entry>
5254        <structfield>typcategory</structfield> is an arbitrary classification
5255        of data types that is used by the parser to determine which implicit
5256        casts should be <quote>preferred</>.
5257        See <xref linkend="catalog-typcategory-table">
5258       </entry>
5259      </row>
5260
5261      <row>
5262       <entry><structfield>typispreferred</structfield></entry>
5263       <entry><type>bool</type></entry>
5264       <entry></entry>
5265       <entry>
5266        True if the type is a preferred cast target within its
5267        <structfield>typcategory</structfield>
5268       </entry>
5269      </row>
5270
5271      <row>
5272       <entry><structfield>typisdefined</structfield></entry>
5273       <entry><type>bool</type></entry>
5274       <entry></entry>
5275       <entry>
5276        True if the type is defined, false if this is a placeholder
5277        entry for a not-yet-defined type.  When
5278        <structfield>typisdefined</structfield> is false, nothing
5279        except the type name, namespace, and OID can be relied on
5280       </entry>
5281      </row>
5282
5283      <row>
5284       <entry><structfield>typdelim</structfield></entry>
5285       <entry><type>char</type></entry>
5286       <entry></entry>
5287       <entry>
5288        Character that separates two values of this type when parsing
5289        array input.  Note that the delimiter is associated with the array
5290        element data type, not the array data type
5291       </entry>
5292      </row>
5293
5294      <row>
5295       <entry><structfield>typrelid</structfield></entry>
5296       <entry><type>oid</type></entry>
5297       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
5298       <entry>
5299        If this is a composite type (see
5300        <structfield>typtype</structfield>), then this column points to
5301        the <structname>pg_class</structname> entry that defines the
5302        corresponding table.  (For a free-standing composite type, the
5303        <structname>pg_class</structname> entry doesn't really represent
5304        a table, but it is needed anyway for the type's
5305        <structname>pg_attribute</structname> entries to link to.)
5306        Zero for non-composite types
5307       </entry>
5308      </row>
5309
5310      <row>
5311       <entry><structfield>typelem</structfield></entry>
5312       <entry><type>oid</type></entry>
5313       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
5314       <entry>
5315        If <structfield>typelem</structfield> is not 0 then it
5316        identifies another row in <structname>pg_type</structname>.
5317        The current type can then be subscripted like an array yielding
5318        values of type <structfield>typelem</structfield>.  A
5319        <quote>true</quote> array type is variable length
5320        (<structfield>typlen</structfield> = -1),
5321        but some fixed-length (<structfield>typlen</structfield> &gt; 0) types
5322        also have nonzero <structfield>typelem</structfield>, for example
5323        <type>name</type> and <type>point</type>.
5324        If a fixed-length type has a <structfield>typelem</structfield> then
5325        its internal representation must be some number of values of the
5326        <structfield>typelem</structfield> data type with no other data.
5327        Variable-length array types have a header defined by the array
5328        subroutines
5329       </entry>
5330      </row>
5331
5332      <row>
5333       <entry><structfield>typarray</structfield></entry>
5334       <entry><type>oid</type></entry>
5335       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
5336       <entry>
5337        If <structfield>typarray</structfield> is not 0 then it
5338        identifies another row in <structname>pg_type</structname>, which
5339        is the <quote>true</quote> array type having this type as element
5340       </entry>
5341      </row>
5342
5343      <row>
5344       <entry><structfield>typinput</structfield></entry>
5345       <entry><type>regproc</type></entry>
5346       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5347       <entry>Input conversion function (text format)</entry>
5348      </row>
5349
5350      <row>
5351       <entry><structfield>typoutput</structfield></entry>
5352       <entry><type>regproc</type></entry>
5353       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5354       <entry>Output conversion function (text format)</entry>
5355      </row>
5356
5357      <row>
5358       <entry><structfield>typreceive</structfield></entry>
5359       <entry><type>regproc</type></entry>
5360       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5361       <entry>Input conversion function (binary format), or 0 if none</entry>
5362      </row>
5363
5364      <row>
5365       <entry><structfield>typsend</structfield></entry>
5366       <entry><type>regproc</type></entry>
5367       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5368       <entry>Output conversion function (binary format), or 0 if none</entry>
5369      </row>
5370
5371      <row>
5372       <entry><structfield>typmodin</structfield></entry>
5373       <entry><type>regproc</type></entry>
5374       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5375       <entry>Type modifier input function, or 0 if type does not support modifiers</entry>
5376      </row>
5377
5378      <row>
5379       <entry><structfield>typmodout</structfield></entry>
5380       <entry><type>regproc</type></entry>
5381       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5382       <entry>Type modifier output function, or 0 to use the standard format</entry>
5383      </row>
5384
5385      <row>
5386       <entry><structfield>typanalyze</structfield></entry>
5387       <entry><type>regproc</type></entry>
5388       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5389       <entry>Custom ANALYZE function, or 0 to use the standard function</entry>
5390      </row>
5391
5392      <row>
5393       <entry><structfield>typalign</structfield></entry>
5394       <entry><type>char</type></entry>
5395       <entry></entry>
5396       <entry><para>
5397
5398        <structfield>typalign</structfield> is the alignment required
5399        when storing a value of this type.  It applies to storage on
5400        disk as well as most representations of the value inside
5401        <productname>PostgreSQL</>.
5402        When multiple values are stored consecutively, such
5403        as in the representation of a complete row on disk, padding is
5404        inserted before a datum of this type so that it begins on the
5405        specified boundary.  The alignment reference is the beginning
5406        of the first datum in the sequence.
5407       </para><para>
5408        Possible values are:
5409        <itemizedlist>
5410         <listitem>
5411          <para><literal>c</> = <type>char</type> alignment, i.e., no alignment needed.</para>
5412         </listitem>
5413         <listitem>
5414          <para><literal>s</> = <type>short</type> alignment (2 bytes on most machines).</para>
5415         </listitem>
5416         <listitem>
5417          <para><literal>i</> = <type>int</type> alignment (4 bytes on most machines).</para>
5418         </listitem>
5419         <listitem>
5420          <para><literal>d</> = <type>double</type> alignment (8 bytes on many machines, but by no means all).</para>
5421         </listitem>
5422        </itemizedlist>
5423       </para><note>
5424        <para>
5425         For types used in system tables, it is critical that the size
5426         and alignment defined in <structname>pg_type</structname>
5427         agree with the way that the compiler will lay out the column in
5428         a structure representing a table row.
5429        </para>
5430       </note></entry>
5431      </row>
5432
5433      <row>
5434       <entry><structfield>typstorage</structfield></entry>
5435       <entry><type>char</type></entry>
5436       <entry></entry>
5437       <entry><para>
5438        <structfield>typstorage</structfield> tells for varlena
5439        types (those with <structfield>typlen</structfield> = -1) if
5440        the type is prepared for toasting and what the default strategy
5441        for attributes of this type should be.
5442        Possible values are
5443        <itemizedlist>
5444         <listitem>
5445          <para><literal>p</>: Value must always be stored plain.</para>
5446         </listitem>
5447         <listitem>
5448          <para>
5449           <literal>e</>: Value can be stored in a <quote>secondary</quote>
5450           relation (if relation has one, see
5451           <literal>pg_class.reltoastrelid</literal>).
5452          </para>
5453         </listitem>
5454         <listitem>
5455          <para><literal>m</>: Value can be stored compressed inline.</para>
5456         </listitem>
5457         <listitem>
5458          <para><literal>x</>: Value can be stored compressed inline or stored in <quote>secondary</quote> storage.</para>
5459         </listitem>
5460        </itemizedlist>
5461        Note that <literal>m</> columns can also be moved out to secondary
5462        storage, but only as a last resort (<literal>e</> and <literal>x</> columns are
5463        moved first).
5464       </para></entry>
5465      </row>
5466
5467      <row>
5468       <entry><structfield>typnotnull</structfield></entry>
5469       <entry><type>bool</type></entry>
5470       <entry></entry>
5471       <entry><para>
5472        <structfield>typnotnull</structfield> represents a not-null
5473        constraint on a type.  Used for domains only
5474       </para></entry>
5475      </row>
5476
5477      <row>
5478       <entry><structfield>typbasetype</structfield></entry>
5479       <entry><type>oid</type></entry>
5480       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
5481       <entry><para>
5482        If this is a domain (see <structfield>typtype</structfield>), then
5483        <structfield>typbasetype</structfield> identifies the type that this
5484        one is based on.  Zero if this type is not a domain
5485       </para></entry>
5486      </row>
5487
5488      <row>
5489       <entry><structfield>typtypmod</structfield></entry>
5490       <entry><type>int4</type></entry>
5491       <entry></entry>
5492       <entry><para>
5493        Domains use <structfield>typtypmod</structfield> to record the <literal>typmod</>
5494        to be applied to their base type (-1 if base type does not use a
5495        <literal>typmod</>).  -1 if this type is not a domain
5496       </para></entry>
5497      </row>
5498
5499      <row>
5500       <entry><structfield>typndims</structfield></entry>
5501       <entry><type>int4</type></entry>
5502       <entry></entry>
5503       <entry><para>
5504        <structfield>typndims</structfield> is the number of array dimensions
5505        for a domain that is an array (that is, <structfield>typbasetype</> is
5506        an array type; the domain's <structfield>typelem</> will match the base
5507        type's <structfield>typelem</structfield>).
5508        Zero for types other than domains over array types
5509        </para></entry>
5510      </row>
5511
5512      <row>
5513       <entry><structfield>typdefaultbin</structfield></entry>
5514       <entry><type>text</type></entry>
5515       <entry></entry>
5516       <entry><para>
5517        If <structfield>typdefaultbin</> is not null, it is the <function>nodeToString()</function>
5518        representation of a default expression for the type.  This is
5519        only used for domains
5520       </para></entry>
5521      </row>
5522
5523      <row>
5524       <entry><structfield>typdefault</structfield></entry>
5525       <entry><type>text</type></entry>
5526       <entry></entry>
5527       <entry><para>
5528        <structfield>typdefault</> is null if the type has no associated
5529        default value. If <structfield>typdefaultbin</> is not null,
5530        <structfield>typdefault</> must contain a human-readable version of the
5531        default expression represented by <structfield>typdefaultbin</>.  If
5532        <structfield>typdefaultbin</> is null and <structfield>typdefault</> is
5533        not, then <structfield>typdefault</> is the external representation of
5534        the type's default value, which might be fed to the type's input
5535        converter to produce a constant
5536       </para></entry>
5537      </row>
5538     </tbody>
5539    </tgroup>
5540   </table>
5541
5542   <para>
5543    <xref linkend="catalog-typcategory-table"> lists the system-defined values
5544    of <structfield>typcategory</>.  Any future additions to this list will
5545    also be upper-case ASCII letters.  All other ASCII characters are reserved
5546    for user-defined categories.
5547   </para>
5548
5549   <table id="catalog-typcategory-table">
5550    <title><structfield>typcategory</> Codes</title>
5551
5552    <tgroup cols=2>
5553     <thead>
5554      <row>
5555       <entry>Code</entry>
5556       <entry>Category</entry>
5557      </row>
5558     </thead>
5559
5560     <tbody>
5561      <row>
5562       <entry><literal>A</literal></entry>
5563       <entry>Array types</entry>
5564      </row>
5565      <row>
5566       <entry><literal>B</literal></entry>
5567       <entry>Boolean types</entry>
5568      </row>
5569      <row>
5570       <entry><literal>C</literal></entry>
5571       <entry>Composite types</entry>
5572      </row>
5573      <row>
5574       <entry><literal>D</literal></entry>
5575       <entry>Date/time types</entry>
5576      </row>
5577      <row>
5578       <entry><literal>E</literal></entry>
5579       <entry>Enum types</entry>
5580      </row>
5581      <row>
5582       <entry><literal>G</literal></entry>
5583       <entry>Geometric types</entry>
5584      </row>
5585      <row>
5586       <entry><literal>I</literal></entry>
5587       <entry>Network address types</entry>
5588      </row>
5589      <row>
5590       <entry><literal>N</literal></entry>
5591       <entry>Numeric types</entry>
5592      </row>
5593      <row>
5594       <entry><literal>P</literal></entry>
5595       <entry>Pseudo-types</entry>
5596      </row>
5597      <row>
5598       <entry><literal>S</literal></entry>
5599       <entry>String types</entry>
5600      </row>
5601      <row>
5602       <entry><literal>T</literal></entry>
5603       <entry>Timespan types</entry>
5604      </row>
5605      <row>
5606       <entry><literal>U</literal></entry>
5607       <entry>User-defined types</entry>
5608      </row>
5609      <row>
5610       <entry><literal>V</literal></entry>
5611       <entry>Bit-string types</entry>
5612      </row>
5613      <row>
5614       <entry><literal>X</literal></entry>
5615       <entry><type>unknown</> type</entry>
5616      </row>
5617     </tbody>
5618    </tgroup>
5619   </table>
5620
5621  </sect1>
5622
5623  <sect1 id="views-overview">
5624   <title>System Views</title>
5625
5626   <para>
5627    In addition to the system catalogs, <productname>PostgreSQL</productname>
5628    provides a number of built-in views.  Some system views provide convenient
5629    access to some commonly used queries on the system catalogs.  Other views
5630    provide access to internal server state.
5631   </para>
5632
5633   <para>
5634    The information schema (<xref linkend="information-schema">) provides
5635    an alternative set of views which overlap the functionality of the system
5636    views.  Since the information schema is SQL-standard whereas the views
5637    described here are <productname>PostgreSQL</productname>-specific,
5638    it's usually better to use the information schema if it provides all
5639    the information you need.
5640   </para>
5641
5642   <para>
5643    <xref linkend="view-table"> lists the system views described here.
5644    More detailed documentation of each view follows below.
5645    There are some additional views that provide access to the results of
5646    the statistics collector; they are described in <xref
5647    linkend="monitoring-stats-views-table">.
5648   </para>
5649
5650   <para>
5651    Except where noted, all the views described here are read-only.
5652   </para>
5653
5654   <table id="view-table">
5655    <title>System Views</title>
5656
5657    <tgroup cols="2">
5658     <thead>
5659      <row>
5660       <entry>View Name</entry>
5661       <entry>Purpose</entry>
5662      </row>
5663     </thead>
5664
5665     <tbody>
5666      <row>
5667       <entry><link linkend="view-pg-cursors"><structname>pg_cursors</structname></link></entry>
5668       <entry>open cursors</entry>
5669      </row>
5670
5671      <row>
5672       <entry><link linkend="view-pg-group"><structname>pg_group</structname></link></entry>
5673       <entry>groups of database users</entry>
5674      </row>
5675
5676      <row>
5677       <entry><link linkend="view-pg-indexes"><structname>pg_indexes</structname></link></entry>
5678       <entry>indexes</entry>
5679      </row>
5680
5681      <row>
5682       <entry><link linkend="view-pg-locks"><structname>pg_locks</structname></link></entry>
5683       <entry>currently held locks</entry>
5684      </row>
5685
5686      <row>
5687       <entry><link linkend="view-pg-prepared-statements"><structname>pg_prepared_statements</structname></link></entry>
5688       <entry>prepared statements</entry>
5689      </row>
5690
5691      <row>
5692       <entry><link linkend="view-pg-prepared-xacts"><structname>pg_prepared_xacts</structname></link></entry>
5693       <entry>prepared transactions</entry>
5694      </row>
5695
5696      <row>
5697       <entry><link linkend="view-pg-roles"><structname>pg_roles</structname></link></entry>
5698       <entry>database roles</entry>
5699      </row>
5700
5701      <row>
5702       <entry><link linkend="view-pg-rules"><structname>pg_rules</structname></link></entry>
5703       <entry>rules</entry>
5704      </row>
5705
5706      <row>
5707       <entry><link linkend="view-pg-settings"><structname>pg_settings</structname></link></entry>
5708       <entry>parameter settings</entry>
5709      </row>
5710
5711      <row>
5712       <entry><link linkend="view-pg-shadow"><structname>pg_shadow</structname></link></entry>
5713       <entry>database users</entry>
5714      </row>
5715
5716      <row>
5717       <entry><link linkend="view-pg-stats"><structname>pg_stats</structname></link></entry>
5718       <entry>planner statistics</entry>
5719      </row>
5720
5721      <row>
5722       <entry><link linkend="view-pg-tables"><structname>pg_tables</structname></link></entry>
5723       <entry>tables</entry>
5724      </row>
5725
5726      <row>
5727       <entry><link linkend="view-pg-timezone-abbrevs"><structname>pg_timezone_abbrevs</structname></link></entry>
5728       <entry>time zone abbreviations</entry>
5729      </row>
5730
5731      <row>
5732       <entry><link linkend="view-pg-timezone-names"><structname>pg_timezone_names</structname></link></entry>
5733       <entry>time zone names</entry>
5734      </row>
5735
5736      <row>
5737       <entry><link linkend="view-pg-user"><structname>pg_user</structname></link></entry>
5738       <entry>database users</entry>
5739      </row>
5740
5741      <row>
5742       <entry><link linkend="view-pg-views"><structname>pg_views</structname></link></entry>
5743       <entry>views</entry>
5744      </row>
5745
5746     </tbody>
5747    </tgroup>
5748   </table>
5749  </sect1>
5750
5751  <sect1 id="view-pg-cursors">
5752   <title><structname>pg_cursors</structname></title>
5753
5754   <indexterm zone="view-pg-cursors">
5755    <primary>pg_cursors</primary>
5756   </indexterm>
5757
5758   <para>
5759    The <structname>pg_cursors</structname> view lists the cursors that
5760    are currently available. Cursors can be defined in several ways:
5761    <itemizedlist>
5762     <listitem>
5763      <para>
5764       via the <xref linkend="sql-declare" endterm="sql-declare-title">
5765       statement in SQL
5766      </para>
5767     </listitem>
5768
5769     <listitem>
5770      <para>
5771       via the Bind message in the frontend/backend protocol, as
5772       described in <xref linkend="protocol-flow-ext-query">
5773      </para>
5774     </listitem>
5775
5776     <listitem>
5777      <para>
5778       via the Server Programming Interface (SPI), as described in
5779       <xref linkend="spi-interface">
5780      </para>
5781     </listitem>
5782    </itemizedlist>
5783
5784    The <structname>pg_cursors</structname> view displays cursors
5785    created by any of these means. Cursors only exist for the duration
5786    of the transaction that defines them, unless they have been
5787    declared <literal>WITH HOLD</literal>. Therefore non-holdable
5788    cursors are only present in the view until the end of their
5789    creating transaction.
5790
5791    <note>
5792     <para>
5793      Cursors are used internally to implement some of the components
5794      of <productname>PostgreSQL</>, such as procedural languages.
5795      Therefore, the <structname>pg_cursors</> view might include cursors
5796      that have not been explicitly created by the user.
5797     </para>
5798    </note>
5799   </para>
5800
5801   <table>
5802    <title><structname>pg_cursors</> Columns</title>
5803
5804    <tgroup cols=3>
5805     <thead>
5806      <row>
5807       <entry>Name</entry>
5808       <entry>Type</entry>
5809       <entry>Description</entry>
5810      </row>
5811     </thead>
5812
5813     <tbody>
5814      <row>
5815       <entry><structfield>name</structfield></entry>
5816       <entry><type>text</type></entry>
5817       <entry>The name of the cursor</entry>
5818      </row>
5819
5820      <row>
5821       <entry><structfield>statement</structfield></entry>
5822       <entry><type>text</type></entry>
5823       <entry>The verbatim query string submitted to declare this cursor</entry>
5824      </row>
5825
5826      <row>
5827       <entry><structfield>is_holdable</structfield></entry>
5828       <entry><type>boolean</type></entry>
5829       <entry>
5830        <literal>true</literal> if the cursor is holdable (that is, it
5831        can be accessed after the transaction that declared the cursor
5832        has committed); <literal>false</literal> otherwise
5833        </entry>
5834      </row>
5835
5836      <row>
5837       <entry><structfield>is_binary</structfield></entry>
5838       <entry><type>boolean</type></entry>
5839       <entry>
5840        <literal>true</literal> if the cursor was declared
5841        <literal>BINARY</literal>; <literal>false</literal>
5842        otherwise
5843        </entry>
5844      </row>
5845
5846      <row>
5847       <entry><structfield>is_scrollable</structfield></entry>
5848       <entry><type>boolean</type></entry>
5849       <entry>
5850        <literal>true</> if the cursor is scrollable (that is, it
5851        allows rows to be retrieved in a nonsequential manner);
5852        <literal>false</literal> otherwise
5853        </entry>
5854      </row>
5855
5856      <row>
5857       <entry><structfield>creation_time</structfield></entry>
5858       <entry><type>timestamptz</type></entry>
5859       <entry>The time at which the cursor was declared</entry>
5860      </row>
5861     </tbody>
5862    </tgroup>
5863   </table>
5864
5865   <para>
5866    The <structname>pg_cursors</structname> view is read only.
5867   </para>
5868
5869  </sect1>
5870
5871  <sect1 id="view-pg-group">
5872   <title><structname>pg_group</structname></title>
5873
5874   <indexterm zone="view-pg-group">
5875    <primary>pg_group</primary>
5876   </indexterm>
5877
5878   <para>
5879    The view <structname>pg_group</structname> exists for backwards
5880    compatibility: it emulates a catalog that existed in
5881    <productname>PostgreSQL</productname> before version 8.1.
5882    It shows the names and members of all roles that are marked as not
5883    <structfield>rolcanlogin</>, which is an approximation to the set
5884    of roles that are being used as groups.
5885   </para>
5886
5887   <table>
5888    <title><structname>pg_group</> Columns</title>
5889
5890    <tgroup cols=4>
5891     <thead>
5892      <row>
5893       <entry>Name</entry>
5894       <entry>Type</entry>
5895       <entry>References</entry>
5896       <entry>Description</entry>
5897      </row>
5898     </thead>
5899
5900     <tbody>
5901      <row>
5902       <entry><structfield>groname</structfield></entry>
5903       <entry><type>name</type></entry>
5904       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
5905       <entry>Name of the group</entry>
5906      </row>
5907
5908      <row>
5909       <entry><structfield>grosysid</structfield></entry>
5910       <entry><type>oid</type></entry>
5911       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
5912       <entry>ID of this group</entry>
5913      </row>
5914
5915      <row>
5916       <entry><structfield>grolist</structfield></entry>
5917       <entry><type>oid[]</type></entry>
5918       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
5919       <entry>An array containing the IDs of the roles in this group</entry>
5920      </row>
5921     </tbody>
5922    </tgroup>
5923   </table>
5924
5925  </sect1>
5926
5927  <sect1 id="view-pg-indexes">
5928   <title><structname>pg_indexes</structname></title>
5929
5930   <indexterm zone="view-pg-indexes">
5931    <primary>pg_indexes</primary>
5932   </indexterm>
5933
5934   <para>
5935    The view <structname>pg_indexes</structname> provides access to
5936    useful information about each index in the database.
5937   </para>
5938
5939   <table>
5940    <title><structname>pg_indexes</> Columns</title>
5941
5942    <tgroup cols=4>
5943     <thead>
5944      <row>
5945       <entry>Name</entry>
5946       <entry>Type</entry>
5947       <entry>References</entry>
5948       <entry>Description</entry>
5949      </row>
5950     </thead>
5951     <tbody>
5952      <row>
5953       <entry><structfield>schemaname</structfield></entry>
5954       <entry><type>name</type></entry>
5955       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
5956       <entry>Name of schema containing table and index</entry>
5957      </row>
5958      <row>
5959       <entry><structfield>tablename</structfield></entry>
5960       <entry><type>name</type></entry>
5961       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
5962       <entry>Name of table the index is for</entry>
5963      </row>
5964      <row>
5965       <entry><structfield>indexname</structfield></entry>
5966       <entry><type>name</type></entry>
5967       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
5968       <entry>Name of index</entry>
5969      </row>
5970      <row>
5971       <entry><structfield>tablespace</structfield></entry>
5972       <entry><type>name</type></entry>
5973       <entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.spcname</literal></entry>
5974       <entry>Name of tablespace containing index (NULL if default for database)</entry>
5975      </row>
5976      <row>
5977       <entry><structfield>indexdef</structfield></entry>
5978       <entry><type>text</type></entry>
5979       <entry></entry>
5980       <entry>Index definition (a reconstructed <command>CREATE INDEX</command>
5981       command)</entry>
5982      </row>
5983     </tbody>
5984    </tgroup>
5985   </table>
5986
5987  </sect1>
5988
5989  <sect1 id="view-pg-locks">
5990   <title><structname>pg_locks</structname></title>
5991
5992   <indexterm zone="view-pg-locks">
5993    <primary>pg_locks</primary>
5994   </indexterm>
5995
5996   <para>
5997    The view <structname>pg_locks</structname> provides access to
5998    information about the locks held by open transactions within the
5999    database server.  See <xref linkend="mvcc"> for more discussion
6000    of locking.
6001   </para>
6002
6003   <para>
6004    <structname>pg_locks</structname> contains one row per active lockable
6005    object, requested lock mode, and relevant transaction.  Thus, the same
6006    lockable object might
6007    appear many times, if multiple transactions are holding or waiting
6008    for locks on it.  However, an object that currently has no locks on it
6009    will not appear at all.
6010   </para>
6011
6012   <para>
6013    There are several distinct types of lockable objects:
6014    whole relations (e.g., tables), individual pages of relations,
6015    individual tuples of relations,
6016    transaction IDs (both virtual and permanent IDs),
6017    and general database objects (identified by class OID and object OID,
6018    in the same way as in <structname>pg_description</structname> or
6019    <structname>pg_depend</structname>).  Also, the right to extend a
6020    relation is represented as a separate lockable object.
6021   </para>
6022
6023   <table>
6024    <title><structname>pg_locks</> Columns</title>
6025
6026    <tgroup cols=4>
6027     <thead>
6028      <row>
6029       <entry>Name</entry>
6030       <entry>Type</entry>
6031       <entry>References</entry>
6032       <entry>Description</entry>
6033      </row>
6034     </thead>
6035     <tbody>
6036      <row>
6037       <entry><structfield>locktype</structfield></entry>
6038       <entry><type>text</type></entry>
6039       <entry></entry>
6040       <entry>
6041        type of the lockable object:
6042        <literal>relation</>,
6043        <literal>extend</>,
6044        <literal>page</>,
6045        <literal>tuple</>,
6046        <literal>transactionid</>,
6047        <literal>virtualxid</>,
6048        <literal>object</>,
6049        <literal>userlock</>, or
6050        <literal>advisory</>
6051       </entry>
6052      </row>
6053      <row>
6054       <entry><structfield>database</structfield></entry>
6055       <entry><type>oid</type></entry>
6056       <entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.oid</literal></entry>
6057       <entry>
6058        OID of the database in which the object exists, or
6059        zero if the object is a shared object, or
6060        NULL if the object is a transaction ID
6061       </entry>
6062      </row>
6063      <row>
6064       <entry><structfield>relation</structfield></entry>
6065       <entry><type>oid</type></entry>
6066       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
6067       <entry>
6068        OID of the relation, or NULL if the object is not
6069        a relation or part of a relation
6070       </entry>
6071      </row>
6072      <row>
6073       <entry><structfield>page</structfield></entry>
6074       <entry><type>integer</type></entry>
6075       <entry></entry>
6076       <entry>
6077        Page number within the relation, or NULL if the object
6078        is not a tuple or relation page
6079       </entry>
6080      </row>
6081      <row>
6082       <entry><structfield>tuple</structfield></entry>
6083       <entry><type>smallint</type></entry>
6084       <entry></entry>
6085       <entry>
6086        Tuple number within the page, or NULL if the object is not a tuple
6087       </entry>
6088      </row>
6089      <row>
6090       <entry><structfield>virtualxid</structfield></entry>
6091       <entry><type>text</type></entry>
6092       <entry></entry>
6093       <entry>
6094        Virtual ID of a transaction, or NULL if the object is not a
6095        virtual transaction ID
6096       </entry>
6097      </row>
6098      <row>
6099       <entry><structfield>transactionid</structfield></entry>
6100       <entry><type>xid</type></entry>
6101       <entry></entry>
6102       <entry>
6103        ID of a transaction, or NULL if the object is not a transaction ID
6104       </entry>
6105      </row>
6106      <row>
6107       <entry><structfield>classid</structfield></entry>
6108       <entry><type>oid</type></entry>
6109       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
6110       <entry>
6111        OID of the system catalog containing the object, or NULL if the
6112        object is not a general database object
6113       </entry>
6114      </row>
6115      <row>
6116       <entry><structfield>objid</structfield></entry>
6117       <entry><type>oid</type></entry>
6118       <entry>any OID column</entry>
6119       <entry>
6120        OID of the object within its system catalog, or NULL if the
6121        object is not a general database object.
6122        For advisory locks it is used to distinguish the two key
6123        spaces (<literal>1</> for an int8 key, <literal>2</> for two
6124        int4 keys).
6125       </entry>
6126      </row>
6127      <row>
6128       <entry><structfield>objsubid</structfield></entry>
6129       <entry><type>smallint</type></entry>
6130       <entry></entry>
6131       <entry>
6132        For a table column, this is the column number (the
6133        <structfield>classid</> and <structfield>objid</> refer to the
6134        table itself).  For all other object types, this column is
6135        zero.  NULL if the object is not a general database object
6136       </entry>
6137      </row>
6138      <row>
6139       <entry><structfield>virtualtransaction</structfield></entry>
6140       <entry><type>text</type></entry>
6141       <entry></entry>
6142       <entry>
6143        Virtual ID of the transaction that is holding or awaiting this lock
6144       </entry>
6145      </row>
6146      <row>
6147       <entry><structfield>pid</structfield></entry>
6148       <entry><type>integer</type></entry>
6149       <entry></entry>
6150       <entry>
6151        Process ID of the server process holding or awaiting this
6152        lock.  NULL if the lock is held by a prepared transaction
6153       </entry>
6154      </row>
6155      <row>
6156       <entry><structfield>mode</structfield></entry>
6157       <entry><type>text</type></entry>
6158       <entry></entry>
6159       <entry>Name of the lock mode held or desired by this process (see <xref
6160       linkend="locking-tables">)</entry>
6161      </row>
6162      <row>
6163       <entry><structfield>granted</structfield></entry>
6164       <entry><type>boolean</type></entry>
6165       <entry></entry>
6166       <entry>True if lock is held, false if lock is awaited</entry>
6167      </row>
6168     </tbody>
6169    </tgroup>
6170   </table>
6171
6172   <para>
6173    <structfield>granted</structfield> is true in a row representing a lock
6174    held by the indicated transaction.  False indicates that this transaction is
6175    currently waiting to acquire this lock, which implies that some other
6176    transaction is holding a conflicting lock mode on the same lockable object.
6177    The waiting transaction will sleep until the other lock is released (or a
6178    deadlock situation is detected). A single transaction can be waiting to
6179    acquire at most one lock at a time.
6180   </para>
6181
6182   <para>
6183    Every transaction holds an exclusive lock on its virtual transaction ID for
6184    its entire duration.  If a permanent ID is assigned to the transaction
6185    (which normally happens only if the transaction changes the state of the
6186    database), it also holds an exclusive lock on its permanent transaction ID
6187    until it ends.  When one transaction finds it necessary to wait specifically
6188    for another transaction, it does so by attempting to acquire share lock on
6189    the other transaction ID (either virtual or permanent ID depending on the
6190    situation). That will succeed only when the other transaction
6191    terminates and releases its locks.
6192   </para>
6193
6194   <para>
6195    Although tuples are a lockable type of object,
6196    information about row-level locks is stored on disk, not in memory,
6197    and therefore row-level locks normally do not appear in this view.
6198    If a transaction is waiting for a
6199    row-level lock, it will usually appear in the view as waiting for the
6200    permanent transaction ID of the current holder of that row lock.
6201   </para>
6202
6203   <para>
6204    Advisory locks can be acquired on keys consisting of either a single
6205    <type>bigint</type> value or two integer values.  A <type>bigint</type> key is displayed with its
6206    high-order half in the <structfield>classid</> column, its low-order half
6207    in the <structfield>objid</> column, and <structfield>objsubid</> equal
6208    to 1.  Integer keys are displayed with the first key in the
6209    <structfield>classid</> column, the second key in the <structfield>objid</>
6210    column, and <structfield>objsubid</> equal to 2.  The actual meaning of
6211    the keys is up to the user.  Advisory locks are local to each database,
6212    so the <structfield>database</> column is meaningful for an advisory lock.
6213   </para>
6214
6215   <para>
6216    When the <structname>pg_locks</structname> view is accessed, the
6217    internal lock manager data structures are momentarily locked, and
6218    a copy is made for the view to display.  This ensures that the
6219    view produces a consistent set of results, while not blocking
6220    normal lock manager operations longer than necessary.  Nonetheless
6221    there could be some impact on database performance if this view is
6222    frequently accessed.
6223   </para>
6224
6225   <para>
6226    <structname>pg_locks</structname> provides a global view of all locks
6227    in the database cluster, not only those relevant to the current database.
6228    Although its <structfield>relation</structfield> column can be joined
6229    against <structname>pg_class</>.<structfield>oid</> to identify locked
6230    relations, this will only work correctly for relations in the current
6231    database (those for which the <structfield>database</structfield> column
6232    is either the current database's OID or zero).
6233   </para>
6234
6235   <para>
6236    The <structfield>pid</structfield> column can be joined to the
6237    <structfield>procpid</structfield> column of the
6238    <structname>pg_stat_activity</structname> view to get more
6239    information on the session holding or waiting to hold each lock.
6240    Also, if you are using prepared transactions, the
6241    <structfield>transaction</> column can be joined to the
6242    <structfield>transaction</structfield> column of the
6243    <structname>pg_prepared_xacts</structname> view to get more
6244    information on prepared transactions that hold locks.
6245    (A prepared transaction can never be waiting for a lock,
6246    but it continues to hold the locks it acquired while running.)
6247   </para>
6248
6249  </sect1>
6250
6251  <sect1 id="view-pg-prepared-statements">
6252   <title><structname>pg_prepared_statements</structname></title>
6253
6254   <indexterm zone="view-pg-prepared-statements">
6255    <primary>pg_prepared_statements</primary>
6256   </indexterm>
6257
6258   <para>
6259    The <structname>pg_prepared_statements</structname> view displays
6260    all the prepared statements that are available in the current
6261    session. See <xref linkend="sql-prepare"
6262    endterm="sql-prepare-title"> for more information about prepared
6263    statements.
6264   </para>
6265
6266   <para>
6267    <structname>pg_prepared_statements</structname> contains one row
6268    for each prepared statement. Rows are added to the view when a new
6269    prepared statement is created and removed when a prepared statement
6270    is released (for example, via the <xref linkend="sql-deallocate"
6271    endterm="sql-deallocate-title"> command).
6272   </para>
6273
6274   <table>
6275    <title><structname>pg_prepared_statements</> Columns</title>
6276
6277    <tgroup cols=3>
6278     <thead>
6279      <row>
6280       <entry>Name</entry>
6281       <entry>Type</entry>
6282       <entry>Description</entry>
6283      </row>
6284     </thead>
6285     <tbody>
6286      <row>
6287       <entry><structfield>name</structfield></entry>
6288       <entry><type>text</type></entry>
6289       <entry>
6290        The identifier of the prepared statement
6291       </entry>
6292      </row>
6293      <row>
6294       <entry><structfield>statement</structfield></entry>
6295       <entry><type>text</type></entry>
6296       <entry>
6297        The query string submitted by the client to create this
6298        prepared statement. For prepared statements created via SQL,
6299        this is the <command>PREPARE</command> statement submitted by
6300        the client. For prepared statements created via the
6301        frontend/backend protocol, this is the text of the prepared
6302        statement itself
6303       </entry>
6304      </row>
6305      <row>
6306       <entry><structfield>prepare_time</structfield></entry>
6307       <entry><type>timestamptz</type></entry>
6308       <entry>
6309        The time at which the prepared statement was created
6310       </entry>
6311      </row>
6312      <row>
6313       <entry><structfield>parameter_types</structfield></entry>
6314       <entry><type>regtype[]</type></entry>
6315       <entry>
6316        The expected parameter types for the prepared statement in the
6317        form of an array of <type>regtype</type>. The OID corresponding
6318        to an element of this array can be obtained by casting the
6319        <type>regtype</type> value to <type>oid</type>
6320       </entry>
6321      </row>
6322      <row>
6323       <entry><structfield>from_sql</structfield></entry>
6324       <entry><type>boolean</type></entry>
6325       <entry>
6326        <literal>true</literal> if the prepared statement was created
6327        via the <command>PREPARE</command> SQL statement;
6328        <literal>false</literal> if the statement was prepared via the
6329        frontend/backend protocol
6330       </entry>
6331      </row>
6332     </tbody>
6333    </tgroup>
6334   </table>
6335
6336   <para>
6337    The <structname>pg_prepared_statements</structname> view is read only.
6338   </para>
6339  </sect1>
6340
6341  <sect1 id="view-pg-prepared-xacts">
6342   <title><structname>pg_prepared_xacts</structname></title>
6343
6344   <indexterm zone="view-pg-prepared-xacts">
6345    <primary>pg_prepared_xacts</primary>
6346   </indexterm>
6347
6348   <para>
6349    The view <structname>pg_prepared_xacts</structname> displays
6350    information about transactions that are currently prepared for two-phase
6351    commit (see <xref linkend="sql-prepare-transaction"
6352    endterm="sql-prepare-transaction-title"> for details).
6353   </para>
6354
6355   <para>
6356    <structname>pg_prepared_xacts</structname> contains one row per prepared
6357    transaction.  An entry is removed when the transaction is committed or
6358    rolled back.
6359   </para>
6360
6361   <table>
6362    <title><structname>pg_prepared_xacts</> Columns</title>
6363
6364    <tgroup cols=4>
6365     <thead>
6366      <row>
6367       <entry>Name</entry>
6368       <entry>Type</entry>
6369       <entry>References</entry>
6370       <entry>Description</entry>
6371      </row>
6372     </thead>
6373     <tbody>
6374      <row>
6375       <entry><structfield>transaction</structfield></entry>
6376       <entry><type>xid</type></entry>
6377       <entry></entry>
6378       <entry>
6379        Numeric transaction identifier of the prepared transaction
6380       </entry>
6381      </row>
6382      <row>
6383       <entry><structfield>gid</structfield></entry>
6384       <entry><type>text</type></entry>
6385       <entry></entry>
6386       <entry>
6387        Global transaction identifier that was assigned to the transaction
6388       </entry>
6389      </row>
6390      <row>
6391       <entry><structfield>prepared</structfield></entry>
6392       <entry><type>timestamp with time zone</type></entry>
6393       <entry></entry>
6394       <entry>
6395        Time at which the transaction was prepared for commit
6396       </entry>
6397      </row>
6398      <row>
6399       <entry><structfield>owner</structfield></entry>
6400       <entry><type>name</type></entry>
6401       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
6402       <entry>
6403        Name of the user that executed the transaction
6404       </entry>
6405      </row>
6406      <row>
6407       <entry><structfield>database</structfield></entry>
6408       <entry><type>name</type></entry>
6409       <entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.datname</literal></entry>
6410       <entry>
6411        Name of the database in which the transaction was executed
6412       </entry>
6413      </row>
6414     </tbody>
6415    </tgroup>
6416   </table>
6417
6418   <para>
6419    When the <structname>pg_prepared_xacts</structname> view is accessed, the
6420    internal transaction manager data structures are momentarily locked, and
6421    a copy is made for the view to display.  This ensures that the
6422    view produces a consistent set of results, while not blocking
6423    normal operations longer than necessary.  Nonetheless
6424    there could be some impact on database performance if this view is
6425    frequently accessed.
6426   </para>
6427
6428  </sect1>
6429
6430  <sect1 id="view-pg-roles">
6431   <title><structname>pg_roles</structname></title>
6432
6433   <indexterm zone="view-pg-roles">
6434    <primary>pg_roles</primary>
6435   </indexterm>
6436
6437   <para>
6438    The view <structname>pg_roles</structname> provides access to
6439    information about database roles.  This is simply a publicly
6440    readable view of
6441    <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>
6442    that blanks out the password field.
6443   </para>
6444
6445   <para>
6446    This view explicitly exposes the OID column of the underlying table,
6447    since that is needed to do joins to other catalogs.
6448   </para>
6449
6450   <table>
6451    <title><structname>pg_roles</> Columns</title>
6452
6453    <tgroup cols=4>
6454     <thead>
6455      <row>
6456       <entry>Name</entry>
6457       <entry>Type</entry>
6458       <entry>References</entry>
6459       <entry>Description</entry>
6460      </row>
6461     </thead>
6462
6463     <tbody>
6464      <row>
6465       <entry><structfield>rolname</structfield></entry>
6466       <entry><type>name</type></entry>
6467       <entry></entry>
6468       <entry>Role name</entry>
6469      </row>
6470
6471      <row>
6472       <entry><structfield>rolsuper</structfield></entry>
6473       <entry><type>bool</type></entry>
6474       <entry></entry>
6475       <entry>Role has superuser privileges</entry>
6476      </row>
6477
6478      <row>
6479       <entry><structfield>rolinherit</structfield></entry>
6480       <entry><type>bool</type></entry>
6481       <entry></entry>
6482       <entry>Role automatically inherits privileges of roles it is a
6483        member of</entry>
6484      </row>
6485
6486      <row>
6487       <entry><structfield>rolcreaterole</structfield></entry>
6488       <entry><type>bool</type></entry>
6489       <entry></entry>
6490       <entry>Role can create more roles</entry>
6491      </row>
6492
6493      <row>
6494       <entry><structfield>rolcreatedb</structfield></entry>
6495       <entry><type>bool</type></entry>
6496       <entry></entry>
6497       <entry>Role can create databases</entry>
6498      </row>
6499
6500      <row>
6501       <entry><structfield>rolcatupdate</structfield></entry>
6502       <entry><type>bool</type></entry>
6503       <entry></entry>
6504       <entry>
6505        Role can update system catalogs directly.  (Even a superuser cannot do
6506        this unless this column is true.)
6507       </entry>
6508      </row>
6509
6510      <row>
6511       <entry><structfield>rolcanlogin</structfield></entry>
6512       <entry><type>bool</type></entry>
6513       <entry></entry>
6514       <entry>
6515        Role can log in. That is, this role can be given as the initial
6516        session authorization identifier
6517       </entry>
6518      </row>
6519
6520      <row>
6521       <entry><structfield>rolconnlimit</structfield></entry>
6522       <entry><type>int4</type></entry>
6523       <entry></entry>
6524       <entry>
6525        For roles that can log in, this sets maximum number of concurrent
6526        connections this role can make.  -1 means no limit
6527       </entry>
6528      </row>
6529
6530      <row>
6531       <entry><structfield>rolpassword</structfield></entry>
6532       <entry><type>text</type></entry>
6533       <entry></entry>
6534       <entry>Not the password (always reads as <literal>********</>)</entry>
6535      </row>
6536
6537      <row>
6538       <entry><structfield>rolvaliduntil</structfield></entry>
6539       <entry><type>timestamptz</type></entry>
6540       <entry></entry>
6541       <entry>Password expiry time (only used for password authentication);
6542        NULL if no expiration</entry>
6543      </row>
6544
6545      <row>
6546       <entry><structfield>rolconfig</structfield></entry>
6547       <entry><type>text[]</type></entry>
6548       <entry></entry>
6549       <entry>Session defaults for run-time configuration variables</entry>
6550      </row>
6551
6552      <row>
6553       <entry><structfield>oid</structfield></entry>
6554       <entry><type>oid</type></entry>
6555       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
6556       <entry>ID of role</entry>
6557      </row>
6558     </tbody>
6559    </tgroup>
6560   </table>
6561
6562  </sect1>
6563
6564  <sect1 id="view-pg-rules">
6565   <title><structname>pg_rules</structname></title>
6566
6567   <indexterm zone="view-pg-rules">
6568    <primary>pg_rules</primary>
6569   </indexterm>
6570
6571   <para>
6572    The view <structname>pg_rules</structname> provides access to
6573    useful information about query rewrite rules.
6574   </para>
6575
6576   <table>
6577    <title><structname>pg_rules</> Columns</title>
6578
6579    <tgroup cols=4>
6580     <thead>
6581      <row>
6582       <entry>Name</entry>
6583       <entry>Type</entry>
6584       <entry>References</entry>
6585       <entry>Description</entry>
6586      </row>
6587     </thead>
6588     <tbody>
6589      <row>
6590       <entry><structfield>schemaname</structfield></entry>
6591       <entry><type>name</type></entry>
6592       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
6593       <entry>Name of schema containing table</entry>
6594      </row>
6595      <row>
6596       <entry><structfield>tablename</structfield></entry>
6597       <entry><type>name</type></entry>
6598       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
6599       <entry>Name of table the rule is for</entry>
6600      </row>
6601      <row>
6602       <entry><structfield>rulename</structfield></entry>
6603       <entry><type>name</type></entry>
6604       <entry><literal><link linkend="catalog-pg-rewrite"><structname>pg_rewrite</structname></link>.rulename</literal></entry>
6605       <entry>Name of rule</entry>
6606      </row>
6607      <row>
6608       <entry><structfield>definition</structfield></entry>
6609       <entry><type>text</type></entry>
6610       <entry></entry>
6611       <entry>Rule definition (a reconstructed creation command)</entry>
6612      </row>
6613     </tbody>
6614    </tgroup>
6615   </table>
6616
6617   <para>
6618    The <structname>pg_rules</> view excludes the <literal>ON SELECT</> rules
6619    of views; those can be seen in <structname>pg_views</>.
6620   </para>
6621
6622  </sect1>
6623
6624  <sect1 id="view-pg-settings">
6625   <title><structname>pg_settings</structname></title>
6626
6627   <indexterm zone="view-pg-settings">
6628    <primary>pg_settings</primary>
6629   </indexterm>
6630
6631   <para>
6632    The view <structname>pg_settings</structname> provides access to
6633    run-time parameters of the server.  It is essentially an alternative
6634    interface to the <xref linkend="sql-show" endterm="sql-show-title">
6635    and <xref linkend="sql-set" endterm="sql-set-title"> commands.
6636    It also provides access to some facts about each parameter that are
6637    not directly available from <command>SHOW</>, such as minimum and
6638    maximum values.
6639   </para>
6640
6641   <table>
6642    <title><structname>pg_settings</> Columns</title>
6643
6644    <tgroup cols=3>
6645     <thead>
6646      <row>
6647       <entry>Name</entry>
6648       <entry>Type</entry>
6649       <entry>Description</entry>
6650      </row>
6651     </thead>
6652     <tbody>
6653      <row>
6654       <entry><structfield>name</structfield></entry>
6655       <entry><type>text</type></entry>
6656       <entry>Run-time configuration parameter name</entry>
6657      </row>
6658      <row>
6659       <entry><structfield>setting</structfield></entry>
6660       <entry><type>text</type></entry>
6661       <entry>Current value of the parameter</entry>
6662      </row>
6663      <row>
6664       <entry><structfield>unit</structfield></entry>
6665       <entry><type>text</type></entry>
6666       <entry>Implicit unit of the parameter</entry>
6667      </row>
6668      <row>
6669       <entry><structfield>category</structfield></entry>
6670       <entry><type>text</type></entry>
6671       <entry>Logical group of the parameter</entry>
6672      </row>
6673      <row>
6674       <entry><structfield>short_desc</structfield></entry>
6675       <entry><type>text</type></entry>
6676       <entry>A brief description of the parameter</entry>
6677      </row>
6678      <row>
6679       <entry><structfield>extra_desc</structfield></entry>
6680       <entry><type>text</type></entry>
6681       <entry>Additional, more detailed, description of the parameter</entry>
6682      </row>
6683      <row>
6684       <entry><structfield>context</structfield></entry>
6685       <entry><type>text</type></entry>
6686       <entry>Context required to set the parameter's value</entry>
6687      </row>
6688      <row>
6689       <entry><structfield>vartype</structfield></entry>
6690       <entry><type>text</type></entry>
6691       <entry>Parameter type (<literal>bool</>, <literal>enum</>,
6692        <literal>integer</>, <literal>real</>, or <literal>string</>)
6693       </entry>
6694      </row>
6695      <row>
6696       <entry><structfield>source</structfield></entry>
6697       <entry><type>text</type></entry>
6698       <entry>Source of the current parameter value</entry>
6699      </row>
6700      <row>
6701       <entry><structfield>min_val</structfield></entry>
6702       <entry><type>text</type></entry>
6703       <entry>Minimum allowed value of the parameter (NULL for non-numeric
6704       values)</entry>
6705      </row>
6706      <row>
6707       <entry><structfield>max_val</structfield></entry>
6708       <entry><type>text</type></entry>
6709       <entry>Maximum allowed value of the parameter (NULL for non-numeric
6710       values)</entry>
6711      </row>
6712      <row>
6713       <entry><structfield>enumvals</structfield></entry>
6714       <entry><type>text[]</type></entry>
6715       <entry>Allowed values of an enum parameter (NULL for non-enum
6716       values)</entry>
6717      </row>
6718      <row>
6719       <entry><structfield>boot_val</structfield></entry>
6720       <entry><type>text</type></entry>
6721       <entry>Parameter value assumed at server startup if the parameter is
6722       not otherwise set</entry>
6723      </row>
6724      <row>
6725       <entry><structfield>reset_val</structfield></entry>
6726       <entry><type>text</type></entry>
6727       <entry>Value that <command>RESET</command> would reset the parameter to
6728       in the current session</entry>
6729      </row>
6730      <row>
6731       <entry><structfield>sourcefile</structfield></entry>
6732       <entry><type>text</type></entry>
6733       <entry>Configuration file the current value was set in (NULL for
6734       values set from sources other than configuration files, or when
6735       examined by a non-superuser).
6736       Helpful when using configuration include directives</entry>
6737      </row>
6738      <row>
6739       <entry><structfield>sourceline</structfield></entry>
6740       <entry><type>integer</type></entry>
6741       <entry>Line number within the configuration file the current value was
6742       set at (NULL for values set from sources other than configuration files,
6743       or when examined by a non-superuser)
6744       </entry>
6745      </row>
6746     </tbody>
6747    </tgroup>
6748   </table>
6749
6750   <para>
6751    The <structname>pg_settings</structname> view cannot be inserted into or
6752    deleted from, but it can be updated.  An <command>UPDATE</command> applied
6753    to a row of <structname>pg_settings</structname> is equivalent to executing
6754    the <xref linkend="sql-set" endterm="sql-set-title"> command on that named
6755    parameter. The change only affects the value used by the current
6756    session. If an <command>UPDATE</command> is issued within a transaction
6757    that is later aborted, the effects of the <command>UPDATE</command> command
6758    disappear when the transaction is rolled back. Once the surrounding
6759    transaction is committed, the effects will persist until the end of the
6760    session, unless overridden by another <command>UPDATE</command> or
6761    <command>SET</command>.
6762   </para>
6763
6764  </sect1>
6765
6766  <sect1 id="view-pg-shadow">
6767   <title><structname>pg_shadow</structname></title>
6768
6769   <indexterm zone="view-pg-shadow">
6770    <primary>pg_shadow</primary>
6771   </indexterm>
6772
6773   <para>
6774    The view <structname>pg_shadow</structname> exists for backwards
6775    compatibility: it emulates a catalog that existed in
6776    <productname>PostgreSQL</productname> before version 8.1.
6777    It shows properties of all roles that are marked as
6778    <structfield>rolcanlogin</>.
6779   </para>
6780
6781   <para>
6782    The name stems from the fact that this table
6783    should not be readable by the public since it contains passwords.
6784    <link linkend="view-pg-user"><structname>pg_user</structname></link>
6785    is a publicly readable view on
6786    <structname>pg_shadow</structname> that blanks out the password field.
6787   </para>
6788
6789   <table>
6790    <title><structname>pg_shadow</> Columns</title>
6791
6792    <tgroup cols=4>
6793     <thead>
6794      <row>
6795       <entry>Name</entry>
6796       <entry>Type</entry>
6797       <entry>References</entry>
6798       <entry>Description</entry>
6799      </row>
6800     </thead>
6801
6802     <tbody>
6803      <row>
6804       <entry><structfield>usename</structfield></entry>
6805       <entry><type>name</type></entry>
6806       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
6807       <entry>User name</entry>
6808      </row>
6809
6810      <row>
6811       <entry><structfield>usesysid</structfield></entry>
6812       <entry><type>oid</type></entry>
6813       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
6814       <entry>ID of this user</entry>
6815      </row>
6816
6817      <row>
6818       <entry><structfield>usecreatedb</structfield></entry>
6819       <entry><type>bool</type></entry>
6820       <entry></entry>
6821       <entry>User can create databases</entry>
6822      </row>
6823
6824      <row>
6825       <entry><structfield>usesuper</structfield></entry>
6826       <entry><type>bool</type></entry>
6827       <entry></entry>
6828       <entry>User is a superuser</entry>
6829      </row>
6830
6831      <row>
6832       <entry><structfield>usecatupd</structfield></entry>
6833       <entry><type>bool</type></entry>
6834       <entry></entry>
6835       <entry>
6836        User can update system catalogs.  (Even a superuser cannot do
6837        this unless this column is true.)
6838       </entry>
6839      </row>
6840
6841      <row>
6842       <entry><structfield>passwd</structfield></entry>
6843       <entry><type>text</type></entry>
6844       <entry></entry>
6845       <entry>Password (possibly encrypted)</entry>
6846      </row>
6847
6848      <row>
6849       <entry><structfield>valuntil</structfield></entry>
6850       <entry><type>abstime</type></entry>
6851       <entry></entry>
6852       <entry>Password expiry time (only used for password authentication)</entry>
6853      </row>
6854
6855      <row>
6856       <entry><structfield>useconfig</structfield></entry>
6857       <entry><type>text[]</type></entry>
6858       <entry></entry>
6859       <entry>Session defaults for run-time configuration variables</entry>
6860      </row>
6861     </tbody>
6862    </tgroup>
6863   </table>
6864
6865  </sect1>
6866
6867  <sect1 id="view-pg-stats">
6868   <title><structname>pg_stats</structname></title>
6869
6870   <indexterm zone="view-pg-stats">
6871    <primary>pg_stats</primary>
6872   </indexterm>
6873
6874   <para>
6875    The view <structname>pg_stats</structname> provides access to
6876    the information stored in the <link
6877    linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link>
6878    catalog.  This view allows access only to rows of
6879    <structname>pg_statistic</structname> that correspond to tables the
6880    user has permission to read, and therefore it is safe to allow public
6881    read access to this view.
6882   </para>
6883
6884   <para>
6885    <structname>pg_stats</structname> is also designed to present the
6886    information in a more readable format than the underlying catalog
6887    &mdash; at the cost that its schema must be extended whenever new slot types
6888    are defined for <structname>pg_statistic</structname>.
6889   </para>
6890
6891   <table>
6892    <title><structname>pg_stats</> Columns</title>
6893
6894    <tgroup cols=4>
6895     <thead>
6896      <row>
6897       <entry>Name</entry>
6898       <entry>Type</entry>
6899       <entry>References</entry>
6900       <entry>Description</entry>
6901      </row>
6902     </thead>
6903     <tbody>
6904      <row>
6905       <entry><structfield>schemaname</structfield></entry>
6906       <entry><type>name</type></entry>
6907       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
6908       <entry>Name of schema containing table</entry>
6909      </row>
6910
6911      <row>
6912       <entry><structfield>tablename</structfield></entry>
6913       <entry><type>name</type></entry>
6914       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
6915       <entry>Name of table</entry>
6916      </row>
6917
6918      <row>
6919       <entry><structfield>attname</structfield></entry>
6920       <entry><type>name</type></entry>
6921       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attname</literal></entry>
6922       <entry>Name of the column described by this row</entry>
6923      </row>
6924
6925      <row>
6926       <entry><structfield>null_frac</structfield></entry>
6927       <entry><type>real</type></entry>
6928       <entry></entry>
6929       <entry>Fraction of column entries that are null</entry>
6930      </row>
6931
6932      <row>
6933       <entry><structfield>avg_width</structfield></entry>
6934       <entry><type>integer</type></entry>
6935       <entry></entry>
6936       <entry>Average width in bytes of column's entries</entry>
6937      </row>
6938
6939      <row>
6940       <entry><structfield>n_distinct</structfield></entry>
6941       <entry><type>real</type></entry>
6942       <entry></entry>
6943       <entry>
6944        If greater than zero, the estimated number of distinct values in the
6945        column.  If less than zero, the negative of the number of distinct
6946        values divided by the number of rows.  (The negated form is used when
6947        <command>ANALYZE</> believes that the number of distinct values is
6948        likely to increase as the table grows; the positive form is used when
6949        the column seems to have a fixed number of possible values.)  For
6950        example, -1 indicates a unique column in which the number of distinct
6951        values is the same as the number of rows
6952       </entry>
6953      </row>
6954
6955      <row>
6956       <entry><structfield>most_common_vals</structfield></entry>
6957       <entry><type>anyarray</type></entry>
6958       <entry></entry>
6959       <entry>
6960        A list of the most common values in the column. (NULL if
6961        no values seem to be more common than any others.)
6962        For some datatypes such as <type>tsvector</>, this is a list of
6963        the most common element values rather than values of the type itself.
6964       </entry>
6965      </row>
6966
6967      <row>
6968       <entry><structfield>most_common_freqs</structfield></entry>
6969       <entry><type>real[]</type></entry>
6970       <entry></entry>
6971       <entry>
6972        A list of the frequencies of the most common values or elements,
6973        i.e., number of occurrences of each divided by total number of rows.
6974        (NULL when <structfield>most_common_vals</structfield> is.)
6975        For some datatypes such as <type>tsvector</>, it can also store some
6976        additional information, making it longer than the
6977        <structfield>most_common_vals</> array.
6978       </entry>
6979      </row>
6980
6981      <row>
6982       <entry><structfield>histogram_bounds</structfield></entry>
6983       <entry><type>anyarray</type></entry>
6984       <entry></entry>
6985       <entry>
6986        A list of values that divide the column's values into groups of
6987        approximately equal population.  The values in
6988        <structfield>most_common_vals</>, if present, are omitted from this
6989        histogram calculation.  (This column is NULL if the column data type
6990        does not have a <literal>&lt;</> operator or if the
6991        <structfield>most_common_vals</> list accounts for the entire
6992        population.)
6993       </entry>
6994      </row>
6995
6996      <row>
6997       <entry><structfield>correlation</structfield></entry>
6998       <entry><type>real</type></entry>
6999       <entry></entry>
7000       <entry>
7001        Statistical correlation between physical row ordering and
7002        logical ordering of the column values.  This ranges from -1 to +1.
7003        When the value is near -1 or +1, an index scan on the column will
7004        be estimated to be cheaper than when it is near zero, due to reduction
7005        of random access to the disk.  (This column is NULL if the column data
7006        type does not have a <literal>&lt;</> operator.)
7007       </entry>
7008      </row>
7009     </tbody>
7010    </tgroup>
7011   </table>
7012
7013   <para>
7014    The maximum number of entries in the <structfield>most_common_vals</>
7015    and <structfield>histogram_bounds</> arrays can be set on a
7016    column-by-column basis using the <command>ALTER TABLE SET STATISTICS</>
7017    command, or globally by setting the
7018    <xref linkend="guc-default-statistics-target"> run-time parameter.
7019   </para>
7020
7021  </sect1>
7022
7023  <sect1 id="view-pg-tables">
7024   <title><structname>pg_tables</structname></title>
7025
7026   <indexterm zone="view-pg-tables">
7027    <primary>pg_tables</primary>
7028   </indexterm>
7029
7030   <para>
7031    The view <structname>pg_tables</structname> provides access to
7032    useful information about each table in the database.
7033   </para>
7034
7035   <table>
7036    <title><structname>pg_tables</> Columns</title>
7037
7038    <tgroup cols=4>
7039     <thead>
7040      <row>
7041       <entry>Name</entry>
7042       <entry>Type</entry>
7043       <entry>References</entry>
7044       <entry>Description</entry>
7045      </row>
7046     </thead>
7047     <tbody>
7048      <row>
7049       <entry><structfield>schemaname</structfield></entry>
7050       <entry><type>name</type></entry>
7051       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
7052       <entry>Name of schema containing table</entry>
7053      </row>
7054      <row>
7055       <entry><structfield>tablename</structfield></entry>
7056       <entry><type>name</type></entry>
7057       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
7058       <entry>Name of table</entry>
7059      </row>
7060      <row>
7061       <entry><structfield>tableowner</structfield></entry>
7062       <entry><type>name</type></entry>
7063       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
7064       <entry>Name of table's owner</entry>
7065      </row>
7066      <row>
7067       <entry><structfield>tablespace</structfield></entry>
7068       <entry><type>name</type></entry>
7069       <entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.spcname</literal></entry>
7070       <entry>Name of tablespace containing table (NULL if default for database)</entry>
7071      </row>
7072      <row>
7073       <entry><structfield>hasindexes</structfield></entry>
7074       <entry><type>boolean</type></entry>
7075       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relhasindex</literal></entry>
7076       <entry>true if table has (or recently had) any indexes</entry>
7077      </row>
7078      <row>
7079       <entry><structfield>hasrules</structfield></entry>
7080       <entry><type>boolean</type></entry>
7081       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relhasrules</literal></entry>
7082       <entry>true if table has (or once had) rules</entry>
7083      </row>
7084      <row>
7085       <entry><structfield>hastriggers</structfield></entry>
7086       <entry><type>boolean</type></entry>
7087       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relhastriggers</literal></entry>
7088       <entry>true if table has (or once had) triggers</entry>
7089      </row>
7090     </tbody>
7091    </tgroup>
7092   </table>
7093
7094  </sect1>
7095
7096  <sect1 id="view-pg-timezone-abbrevs">
7097   <title><structname>pg_timezone_abbrevs</structname></title>
7098
7099   <indexterm zone="view-pg-timezone-abbrevs">
7100    <primary>pg_timezone_abbrevs</primary>
7101   </indexterm>
7102
7103   <para>
7104    The view <structname>pg_timezone_abbrevs</structname> provides a list
7105    of time zone abbreviations that are currently recognized by the datetime
7106    input routines.  The contents of this view change when the
7107    <xref linkend="guc-timezone-abbreviations"> run-time parameter is modified.
7108   </para>
7109
7110   <table>
7111    <title><structname>pg_timezone_abbrevs</> Columns</title>
7112
7113    <tgroup cols=3>
7114     <thead>
7115      <row>
7116       <entry>Name</entry>
7117       <entry>Type</entry>
7118       <entry>Description</entry>
7119      </row>
7120     </thead>
7121     <tbody>
7122      <row>
7123       <entry><structfield>abbrev</structfield></entry>
7124       <entry><type>text</type></entry>
7125       <entry>Time zone abbreviation</entry>
7126      </row>
7127      <row>
7128       <entry><structfield>utc_offset</structfield></entry>
7129       <entry><type>interval</type></entry>
7130       <entry>Offset from UTC (positive means east of Greenwich)</entry>
7131      </row>
7132      <row>
7133       <entry><structfield>is_dst</structfield></entry>
7134       <entry><type>boolean</type></entry>
7135       <entry>True if this is a daylight-savings abbreviation</entry>
7136      </row>
7137     </tbody>
7138    </tgroup>
7139   </table>
7140
7141  </sect1>
7142
7143  <sect1 id="view-pg-timezone-names">
7144   <title><structname>pg_timezone_names</structname></title>
7145
7146   <indexterm zone="view-pg-timezone-names">
7147    <primary>pg_timezone_names</primary>
7148   </indexterm>
7149
7150   <para>
7151    The view <structname>pg_timezone_names</structname> provides a list
7152    of time zone names that are recognized by <command>SET TIMEZONE</>,
7153    along with their associated abbreviations, UTC offsets,
7154    and daylight-savings status.
7155    Unlike the abbreviations shown in <link
7156    linkend="view-pg-timezone-abbrevs"><structname>pg_timezone_abbrevs</structname></link>, many of these names imply a set of daylight-savings transition
7157    date rules.  Therefore, the associated information changes across local DST
7158    boundaries.  The displayed information is computed based on the current
7159    value of <function>CURRENT_TIMESTAMP</>.
7160   </para>
7161
7162   <table>
7163    <title><structname>pg_timezone_names</> Columns</title>
7164
7165    <tgroup cols=3>
7166     <thead>
7167      <row>
7168       <entry>Name</entry>
7169       <entry>Type</entry>
7170       <entry>Description</entry>
7171      </row>
7172     </thead>
7173     <tbody>
7174      <row>
7175       <entry><structfield>name</structfield></entry>
7176       <entry><type>text</type></entry>
7177       <entry>Time zone name</entry>
7178      </row>
7179      <row>
7180       <entry><structfield>abbrev</structfield></entry>
7181       <entry><type>text</type></entry>
7182       <entry>Time zone abbreviation</entry>
7183      </row>
7184      <row>
7185       <entry><structfield>utc_offset</structfield></entry>
7186       <entry><type>interval</type></entry>
7187       <entry>Offset from UTC (positive means east of Greenwich)</entry>
7188      </row>
7189      <row>
7190       <entry><structfield>is_dst</structfield></entry>
7191       <entry><type>boolean</type></entry>
7192       <entry>True if currently observing daylight savings</entry>
7193      </row>
7194     </tbody>
7195    </tgroup>
7196   </table>
7197
7198  </sect1>
7199
7200  <sect1 id="view-pg-user">
7201   <title><structname>pg_user</structname></title>
7202
7203   <indexterm zone="view-pg-user">
7204    <primary>pg_user</primary>
7205   </indexterm>
7206
7207   <para>
7208    The view <structname>pg_user</structname> provides access to
7209    information about database users.  This is simply a publicly
7210    readable view of
7211    <link linkend="view-pg-shadow"><structname>pg_shadow</structname></link>
7212    that blanks out the password field.
7213   </para>
7214
7215   <table>
7216    <title><structname>pg_user</> Columns</title>
7217
7218    <tgroup cols=3>
7219     <thead>
7220      <row>
7221       <entry>Name</entry>
7222       <entry>Type</entry>
7223       <entry>Description</entry>
7224      </row>
7225     </thead>
7226     <tbody>
7227      <row>
7228       <entry><structfield>usename</structfield></entry>
7229       <entry><type>name</type></entry>
7230       <entry>User name</entry>
7231      </row>
7232
7233      <row>
7234       <entry><structfield>usesysid</structfield></entry>
7235       <entry><type>int4</type></entry>
7236       <entry>User ID (arbitrary number used to reference this user)</entry>
7237      </row>
7238
7239      <row>
7240       <entry><structfield>usecreatedb</structfield></entry>
7241       <entry><type>bool</type></entry>
7242       <entry>User can create databases</entry>
7243      </row>
7244
7245      <row>
7246       <entry><structfield>usesuper</structfield></entry>
7247       <entry><type>bool</type></entry>
7248       <entry>User is a superuser</entry>
7249      </row>
7250
7251      <row>
7252       <entry><structfield>usecatupd</structfield></entry>
7253       <entry><type>bool</type></entry>
7254       <entry>
7255        User can update system catalogs.  (Even a superuser cannot do
7256        this unless this column is true.)
7257       </entry>
7258      </row>
7259
7260      <row>
7261       <entry><structfield>passwd</structfield></entry>
7262       <entry><type>text</type></entry>
7263       <entry>Not the password (always reads as <literal>********</>)</entry>
7264      </row>
7265
7266      <row>
7267       <entry><structfield>valuntil</structfield></entry>
7268       <entry><type>abstime</type></entry>
7269       <entry>Password expiry time (only used for password authentication)</entry>
7270      </row>
7271
7272      <row>
7273       <entry><structfield>useconfig</structfield></entry>
7274       <entry><type>text[]</type></entry>
7275       <entry>Session defaults for run-time configuration variables</entry>
7276      </row>
7277     </tbody>
7278    </tgroup>
7279   </table>
7280
7281  </sect1>
7282
7283  <sect1 id="view-pg-user-mappings">
7284   <title><structname>pg_user_mappings</structname></title>
7285
7286   <indexterm zone="view-pg-user-mappings">
7287    <primary>pg_user_mappings</primary>
7288   </indexterm>
7289
7290   <para>
7291    The view <structname>pg_user_mappings</structname> provides access
7292    to information about user mappings.  This is essentially a publicly
7293    readable view of
7294    <link linkend="catalog-pg-user-mapping"><structname>pg_user_mapping</structname></link>
7295    that leaves out the options field if the user has no rights to use
7296    it.
7297   </para>
7298
7299   <table>
7300    <title><structname>pg_user_mappings</> Columns</title>
7301
7302    <tgroup cols=3>
7303     <thead>
7304      <row>
7305       <entry>Name</entry>
7306       <entry>Type</entry>
7307       <entry>References</entry>
7308       <entry>Description</entry>
7309      </row>
7310     </thead>
7311
7312     <tbody>
7313      <row>
7314       <entry><structfield>umid</structfield></entry>
7315       <entry><type>oid</type></entry>
7316       <entry><literal><link linkend="catalog-pg-user-mapping"><structname>pg_user_mapping</structname></link>.oid</literal></entry>
7317       <entry>OID of the user mapping</entry>
7318      </row>
7319
7320      <row>
7321       <entry><structfield>srvid</structfield></entry>
7322       <entry><type>oid</type></entry>
7323       <entry><literal><link linkend="catalog-pg-foreign-server"><structname>pg_foreign_server</structname></link>.oid</literal></entry>
7324       <entry>
7325        The OID of the foreign server that contains this mapping
7326       </entry>
7327      </row>
7328
7329      <row>
7330       <entry><structfield>srvname</structfield></entry>
7331       <entry><type>text</type></entry>
7332       <entry></entry>
7333       <entry>
7334        Name of the foreign server
7335       </entry>
7336      </row>
7337
7338      <row>
7339       <entry><structfield>umuser</structfield></entry>
7340       <entry><type>oid</type></entry>
7341       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
7342       <entry>OID of the local role being mapped, 0 if the user mapping is public</entry>
7343      </row>
7344
7345      <row>
7346       <entry><structfield>usename</structfield></entry>
7347       <entry><type>name</type></entry>
7348       <entry></entry>
7349       <entry>Name of the local user to be mapped</entry>
7350      </row>
7351
7352      <row>
7353       <entry><structfield>umoptions</structfield></entry>
7354       <entry><type>text[]</type></entry>
7355       <entry></entry>
7356       <entry>
7357        User mapping specific options, as <quote>keyword=value</>
7358        strings, if the current user is the owner of the foreign
7359        server, else null.
7360       </entry>
7361      </row>
7362     </tbody>
7363    </tgroup>
7364   </table>
7365  </sect1>
7366
7367
7368  <sect1 id="view-pg-views">
7369   <title><structname>pg_views</structname></title>
7370
7371   <indexterm zone="view-pg-views">
7372    <primary>pg_views</primary>
7373   </indexterm>
7374
7375   <para>
7376    The view <structname>pg_views</structname> provides access to
7377    useful information about each view in the database.
7378   </para>
7379
7380   <table>
7381    <title><structname>pg_views</> Columns</title>
7382
7383    <tgroup cols=4>
7384     <thead>
7385      <row>
7386       <entry>Name</entry>
7387       <entry>Type</entry>
7388       <entry>References</entry>
7389       <entry>Description</entry>
7390      </row>
7391     </thead>
7392     <tbody>
7393      <row>
7394       <entry><structfield>schemaname</structfield></entry>
7395       <entry><type>name</type></entry>
7396       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
7397       <entry>Name of schema containing view</entry>
7398      </row>
7399      <row>
7400       <entry><structfield>viewname</structfield></entry>
7401       <entry><type>name</type></entry>
7402       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
7403       <entry>Name of view</entry>
7404      </row>
7405      <row>
7406       <entry><structfield>viewowner</structfield></entry>
7407       <entry><type>name</type></entry>
7408       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
7409       <entry>Name of view's owner</entry>
7410      </row>
7411      <row>
7412       <entry><structfield>definition</structfield></entry>
7413       <entry><type>text</type></entry>
7414       <entry></entry>
7415       <entry>View definition (a reconstructed <command>SELECT</command> query)</entry>
7416      </row>
7417     </tbody>
7418    </tgroup>
7419   </table>
7420
7421  </sect1>
7422
7423 </chapter>