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

doc/src/sgml/ref/drop_index.sgml
143 строки4 KB
Michael Paquier
doc: Clarify use of ACCESS EXCLUSIVE lock in various sections
01 апр 2021, 09:28
01 апр 2021, 09:28ffd3391
<!--
doc/src/sgml/ref/drop_index.sgml
PostgreSQL documentation
-->

<refentry id="sql-dropindex">
 <indexterm zone="sql-dropindex">
  <primary>DROP INDEX</primary>
 </indexterm>

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

 <refnamediv>
  <refname>DROP INDEX</refname>
  <refpurpose>remove an index</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
DROP INDEX [ CONCURRENTLY ] [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...] [ CASCADE | RESTRICT ]
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>DROP INDEX</command> drops an existing index from the database
   system. To execute this command you must be the owner of
   the index.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><literal>CONCURRENTLY</literal></term>
    <listitem>
     <para>
      Drop the index without locking out concurrent selects, inserts, updates,
      and deletes on the index's table.  A normal <command>DROP INDEX</command>
      acquires an <literal>ACCESS EXCLUSIVE</literal> lock on the table,
      blocking other accesses until the index drop can be completed.  With
      this option, the command instead waits until conflicting transactions
      have completed.
     </para>
     <para>
      There are several caveats to be aware of when using this option.
      Only one index name can be specified, and the <literal>CASCADE</literal> option
      is not supported.  (Thus, an index that supports a <literal>UNIQUE</literal> or
      <literal>PRIMARY KEY</literal> constraint cannot be dropped this way.)
      Also, regular <command>DROP INDEX</command> commands can be
      performed within a transaction block, but
      <command>DROP INDEX CONCURRENTLY</command> cannot.
      Lastly, indexes on partitioned tables cannot be dropped using this
      option.
     </para>
     <para>
      For temporary tables, <command>DROP INDEX</command> is always
      non-concurrent, as no other session can access them, and
      non-concurrent index drop is cheaper.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>IF EXISTS</literal></term>
    <listitem>
     <para>
      Do not throw an error if the index does not exist. A notice is issued
      in this case.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">name</replaceable></term>
    <listitem>
     <para>
      The name (optionally schema-qualified) of an index to remove.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>CASCADE</literal></term>
    <listitem>
     <para>
      Automatically drop objects that depend on the index,
      and in turn all objects that depend on those objects
      (see <xref linkend="ddl-depend"/>).
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>RESTRICT</literal></term>
    <listitem>
     <para>
      Refuse to drop the index if any objects depend on it.  This is
      the default.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   This command will remove the index <literal>title_idx</literal>:

<programlisting>
DROP INDEX title_idx;
</programlisting></para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   <command>DROP INDEX</command> is a
   <productname>PostgreSQL</productname> language extension.  There
   are no provisions for indexes in the SQL standard.
  </para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-createindex"/></member>
  </simplelist>
 </refsect1>

</refentry>