doc/src/sgml/ref/discard.sgml - master - githubmirror/postgres

doc/src/sgml/ref/discard.sgml
118 строк3 KB
Alvaro Herrera
Fix order of steps in DISCARD ALL documentation
11 июн 2019, 19:22
11 июн 2019, 19:229f05c44
<!--
doc/src/sgml/ref/discard.sgml
PostgreSQL documentation
-->

<refentry id="sql-discard">
 <indexterm zone="sql-discard">
  <primary>DISCARD</primary>
 </indexterm>

 <refmeta>
  <refentrytitle>DISCARD</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>DISCARD</refname>
  <refpurpose>discard session state</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
DISCARD { ALL | PLANS | SEQUENCES | TEMPORARY | TEMP }
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>DISCARD</command> releases internal resources associated with a
   database session.  This command is useful for partially or fully
   resetting the session's state.  There are several subcommands to
   release different types of resources; the <command>DISCARD ALL</command>
   variant subsumes all the others, and also resets additional state.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>

   <varlistentry>
    <term><literal>PLANS</literal></term>
    <listitem>
     <para>
      Releases all cached query plans, forcing re-planning to occur
      the next time the associated prepared statement is used.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SEQUENCES</literal></term>
    <listitem>
     <para>
      Discards all cached sequence-related state,
      including <function>currval()</function>/<function>lastval()</function>
      information and any preallocated sequence values that have not
      yet been returned by <function>nextval()</function>.
      (See <xref linkend="sql-createsequence"/> for a description of
      preallocated sequence values.)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>TEMPORARY</literal> or <literal>TEMP</literal></term>
    <listitem>
     <para>
      Drops all temporary tables created in the current session.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>ALL</literal></term>
    <listitem>
     <para>
      Releases all temporary resources associated with the current
      session and resets the session to its initial state.
      Currently, this has the same effect as executing the following sequence
      of statements:
<programlisting>
CLOSE ALL;
SET SESSION AUTHORIZATION DEFAULT;
RESET ALL;
DEALLOCATE ALL;
UNLISTEN *;
SELECT pg_advisory_unlock_all();
DISCARD PLANS;
DISCARD TEMP;
DISCARD SEQUENCES;
</programlisting></para>
    </listitem>
   </varlistentry>

  </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

   <para>
    <command>DISCARD ALL</command> cannot be executed inside a transaction block.
   </para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   <command>DISCARD</command> is a <productname>PostgreSQL</productname> extension.
  </para>
 </refsect1>
</refentry>