src/include/storage/relfilenode.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * relfilenode.h
   4  *        Physical access information for relations.
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * $PostgreSQL$
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14 #ifndef RELFILENODE_H
  15 #define RELFILENODE_H
  16
  17 /*
  18  * The physical storage of a relation consists of one or more forks. The
  19  * main fork is always created, but in addition to that there can be
  20  * additional forks for storing various metadata. ForkNumber is used when
  21  * we need to refer to a specific fork in a relation.
  22  */
  23 typedef enum ForkNumber
  24 {
  25         InvalidForkNumber = -1,
  26         MAIN_FORKNUM = 0,
  27         FSM_FORKNUM
  28         /*
  29          * NOTE: if you add a new fork, change MAX_FORKNUM below and update the
  30          * forkNames array in catalog.c
  31          */
  32 } ForkNumber;
  33
  34 #define MAX_FORKNUM             FSM_FORKNUM
  35
  36 /*
  37  * RelFileNode must provide all that we need to know to physically access
  38  * a relation. Note, however, that a "physical" relation is comprised of
  39  * multiple files on the filesystem, as each fork is stored as a separate
  40  * file, and each fork can be divided into multiple segments. See md.c.
  41  *
  42  * spcNode identifies the tablespace of the relation.  It corresponds to
  43  * pg_tablespace.oid.
  44  *
  45  * dbNode identifies the database of the relation.      It is zero for
  46  * "shared" relations (those common to all databases of a cluster).
  47  * Nonzero dbNode values correspond to pg_database.oid.
  48  *
  49  * relNode identifies the specific relation.  relNode corresponds to
  50  * pg_class.relfilenode (NOT pg_class.oid, because we need to be able
  51  * to assign new physical files to relations in some situations).
  52  * Notice that relNode is only unique within a particular database.
  53  *
  54  * Note: spcNode must be GLOBALTABLESPACE_OID if and only if dbNode is
  55  * zero.  We support shared relations only in the "global" tablespace.
  56  *
  57  * Note: in pg_class we allow reltablespace == 0 to denote that the
  58  * relation is stored in its database's "default" tablespace (as
  59  * identified by pg_database.dattablespace).  However this shorthand
  60  * is NOT allowed in RelFileNode structs --- the real tablespace ID
  61  * must be supplied when setting spcNode.
  62  */
  63 typedef struct RelFileNode
  64 {
  65         Oid                     spcNode;                /* tablespace */
  66         Oid                     dbNode;                 /* database */
  67         Oid                     relNode;                /* relation */
  68 } RelFileNode;
  69
  70 /*
  71  * Note: RelFileNodeEquals compares relNode first since that is most likely
  72  * to be different in two unequal RelFileNodes.  It is probably redundant
  73  * to compare spcNode if the other two fields are found equal, but do it
  74  * anyway to be sure.
  75  */
  76 #define RelFileNodeEquals(node1, node2) \
  77         ((node1).relNode == (node2).relNode && \
  78          (node1).dbNode == (node2).dbNode && \
  79          (node1).spcNode == (node2).spcNode)
  80
  81 /*
  82  * RelFileFork identifies a particular fork of a relation.
  83  */
  84 typedef struct RelFileFork
  85 {
  86         RelFileNode rnode;
  87         ForkNumber forknum;
  88 } RelFileFork;
  89
  90 #endif   /* RELFILENODE_H */