doc/src/sgml/ref/discard.sgml

   1 <!--
   2 doc/src/sgml/ref/discard.sgml
   3 PostgreSQL documentation
   4 -->
   5
   6 <refentry id="sql-discard">
   7  <indexterm zone="sql-discard">
   8   <primary>DISCARD</primary>
   9  </indexterm>
  10
  11  <refmeta>
  12   <refentrytitle>DISCARD</refentrytitle>
  13   <manvolnum>7</manvolnum>
  14   <refmiscinfo>SQL - Language Statements</refmiscinfo>
  15  </refmeta>
  16
  17  <refnamediv>
  18   <refname>DISCARD</refname>
  19   <refpurpose>discard session state</refpurpose>
  20  </refnamediv>
  21
  22  <refsynopsisdiv>
  23 <synopsis>
  24 DISCARD { ALL | PLANS | SEQUENCES | TEMPORARY | TEMP }
  25 </synopsis>
  26  </refsynopsisdiv>
  27
  28  <refsect1>
  29   <title>Description</title>
  30
  31   <para>
  32    <command>DISCARD</command> releases internal resources associated with a
  33    database session.  This command is useful for partially or fully
  34    resetting the session's state.  There are several subcommands to
  35    release different types of resources; the <command>DISCARD ALL</command>
  36    variant subsumes all the others, and also resets additional state.
  37   </para>
  38  </refsect1>
  39
  40  <refsect1>
  41   <title>Parameters</title>
  42
  43   <variablelist>
  44
  45    <varlistentry>
  46     <term><literal>PLANS</literal></term>
  47     <listitem>
  48      <para>
  49       Releases all cached query plans, forcing re-planning to occur
  50       the next time the associated prepared statement is used.
  51      </para>
  52     </listitem>
  53    </varlistentry>
  54
  55    <varlistentry>
  56     <term><literal>SEQUENCES</literal></term>
  57     <listitem>
  58      <para>
  59       Discards all cached sequence-related state,
  60       including <function>currval()</function>/<function>lastval()</function>
  61       information and any preallocated sequence values that have not
  62       yet been returned by <function>nextval()</function>.
  63       (See <xref linkend="sql-createsequence"/> for a description of
  64       preallocated sequence values.)
  65      </para>
  66     </listitem>
  67    </varlistentry>
  68
  69    <varlistentry>
  70     <term><literal>TEMPORARY</literal> or <literal>TEMP</literal></term>
  71     <listitem>
  72      <para>
  73       Drops all temporary tables created in the current session.
  74      </para>
  75     </listitem>
  76    </varlistentry>
  77
  78    <varlistentry>
  79     <term><literal>ALL</literal></term>
  80     <listitem>
  81      <para>
  82       Releases all temporary resources associated with the current
  83       session and resets the session to its initial state.
  84       Currently, this has the same effect as executing the following sequence
  85       of statements:
  86 <programlisting>
  87 CLOSE ALL;
  88 SET SESSION AUTHORIZATION DEFAULT;
  89 RESET ALL;
  90 DEALLOCATE ALL;
  91 UNLISTEN *;
  92 SELECT pg_advisory_unlock_all();
  93 DISCARD PLANS;
  94 DISCARD TEMP;
  95 DISCARD SEQUENCES;
  96 </programlisting></para>
  97     </listitem>
  98    </varlistentry>
  99
 100   </variablelist>
 101  </refsect1>
 102
 103  <refsect1>
 104   <title>Notes</title>
 105
 106    <para>
 107     <command>DISCARD ALL</command> cannot be executed inside a transaction block.
 108    </para>
 109  </refsect1>
 110
 111  <refsect1>
 112   <title>Compatibility</title>
 113
 114   <para>
 115    <command>DISCARD</command> is a <productname>PostgreSQL</productname> extension.
 116   </para>
 117  </refsect1>
 118 </refentry>