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<refentry id="SQL-VACUUM">
 <refmeta>
  <refentrytitle id="sql-vacuum-title">
   VACUUM
  </refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>
 <refnamediv>
  <refname>
   VACUUM
  </refname>
  <refpurpose>
   Clean and optionally analyze a <productname>Postgres</productname> database
  </refpurpose>
 </refnamediv>
 <refsynopsisdiv>
  <refsynopsisdivinfo>
   <date>2001-07-10</date>
  </refsynopsisdivinfo>
  <synopsis>
VACUUM [ FULL ] [ VERBOSE ] [ <replaceable class="PARAMETER">table</replaceable> ]
VACUUM [ FULL ] [ VERBOSE ] ANALYZE [ <replaceable class="PARAMETER">table</replaceable> [ (<replaceable class="PARAMETER">column</replaceable> [, ...] ) ] ]
  </synopsis>

  <refsect2 id="R2-SQL-VACUUM-1">
   <refsect2info>
    <date>2001-07-10</date>
   </refsect2info>
   <title>
    Inputs
   </title>

   <para>
    <variablelist>
     <varlistentry>
      <term>FULL</term>
      <listitem>
       <para>
        Selects <quote>full</quote> vacuum, which may reclaim more space,
	but takes much longer and exclusively locks the table.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term>VERBOSE</term>
      <listitem>
       <para>
	Prints a detailed vacuum activity report for each table.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term>ANALYZE</term>
      <listitem>
       <para>
	Updates statistics used by the optimizer to
	determine the most efficient way to execute a query.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><replaceable class="PARAMETER">table</replaceable></term>
      <listitem>
       <para>
	The name of a specific table to vacuum. Defaults to all tables
	in the current database.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><replaceable class="PARAMETER">column</replaceable></term>
      <listitem>
       <para>
	The name of a specific column to analyze. Defaults to all columns.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>

  <refsect2 id="R2-SQL-VACUUM-2">
   <refsect2info>
    <date>1998-10-04</date>
   </refsect2info>
   <title>
    Outputs
   </title>
   <para>

    <variablelist>
     <varlistentry>
      <term><computeroutput>
<returnvalue>VACUUM</returnvalue>
       </computeroutput></term>
      <listitem>
       <para>
	The command is complete.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><computeroutput>
NOTICE:  --Relation <replaceable class="PARAMETER">table</replaceable>--
       </computeroutput></term>
      <listitem>
       <para>
	The report header for <replaceable class="PARAMETER">table</replaceable>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><computeroutput>
NOTICE:  Pages 98: Changed 25, Reapped 74, Empty 0, New 0;
         Tup 1000: Vac 3000, Crash 0, UnUsed 0, MinLen 188, MaxLen 188;
         Re-using: Free/Avail. Space 586952/586952; EndEmpty/Avail. Pages 0/74.
         Elapsed 0/0 sec.
       </computeroutput></term>
      <listitem>
       <para>
	The analysis for <replaceable class="PARAMETER">table</replaceable> itself.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><computeroutput>
NOTICE:  Index <replaceable class="PARAMETER">index</replaceable>: Pages 28;
         Tuples 1000: Deleted 3000. Elapsed 0/0 sec.
       </computeroutput></term>
      <listitem>
       <para>
	The analysis for an index on the target table.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>
 </refsynopsisdiv>

 <refsect1 id="R1-SQL-VACUUM-1">
  <refsect1info>
   <date>2001-07-10</date>
  </refsect1info>
  <title>
   Description
  </title>
  <para>
   <command>VACUUM</command> reclaims storage occupied by deleted tuples.
   In normal <productname>Postgres</productname> operation, tuples that
   are DELETEd or obsoleted by UPDATE are not physically removed from
   their table; they remain present until a <command>VACUUM</command> is
   done.  Therefore it's necessary to do <command>VACUUM</command>
   periodically, especially on frequently-updated tables.
  </para>

  <para>
   With no parameter, <command>VACUUM</command> processes every table in the
   current database.  With a parameter, <command>VACUUM</command> processes
   only that table.
  </para>

  <para>
   Plain <command>VACUUM</command> simply reclaims space and makes it
   available for re-use.  This form of the command can operate in parallel
   with normal reading and writing of the table.  <command>VACUUM
   FULL</command> does more extensive processing, including moving of tuples
   across blocks to try to compact the table to the minimum number of disk
   blocks.  This is much slower and requires an exclusive lock on each table
   while it is being processed.
  </para>

  <para>
   <command>VACUUM ANALYZE</command> performs a <command>VACUUM</command>
   and then an <command>ANALYZE</command> for each selected table.  This
   is a handy combination form for routine maintenance scripts.  See
   <xref linkend="sql-analyze" endterm="sql-analyze-title">
   for more details about its processing.
  </para>

  <refsect2 id="R2-SQL-VACUUM-3">
   <refsect2info>
    <date>2001-07-10</date>
   </refsect2info>
   <title>
    Notes
   </title>

   <para>
    We recommend that active production databases be
    <command>VACUUM</command>-ed frequently (at least nightly), in order to
    remove expired rows. After copying a large table into
    <productname>Postgres</productname> or after deleting a large number
    of records, it may be a good idea to issue a <command>VACUUM
    ANALYZE</command> command for the affected table. This will update the
    system catalogs with
    the results of all recent changes, and allow the
    <productname>Postgres</productname> query optimizer to make better
    choices in planning user queries.
   </para>

   <para>
    The <option>FULL</option> option is not recommended for routine use,
    but may be useful in special cases.  An example is when you have deleted
    most of the rows in a table and would like the table to physically shrink
    to occupy less disk space.  <command>VACUUM FULL</command> will usually
    shrink the table more than a plain <command>VACUUM</command> would.
   </para>

  </refsect2>
 </refsect1>

 <refsect1 id="R1-SQL-VACUUM-2">
  <title>
   Usage
  </title>
  <para>
   The following is an example from running <command>VACUUM</command> on a table
   in the regression database:

   <programlisting>
regression=> vacuum verbose analyze onek;
NOTICE:  --Relation onek--
NOTICE:  Pages 98: Changed 25, Reapped 74, Empty 0, New 0;
         Tup 1000: Vac 3000, Crash 0, UnUsed 0, MinLen 188, MaxLen 188;
         Re-using: Free/Avail. Space 586952/586952; EndEmpty/Avail. Pages 0/74.
         Elapsed 0/0 sec.
NOTICE:  Index onek_stringu1: Pages 28; Tuples 1000: Deleted 3000. Elapsed 0/0 sec.
NOTICE:  Index onek_hundred: Pages 12; Tuples 1000: Deleted 3000. Elapsed 0/0 sec.
NOTICE:  Index onek_unique2: Pages 19; Tuples 1000: Deleted 3000. Elapsed 0/0 sec.
NOTICE:  Index onek_unique1: Pages 17; Tuples 1000: Deleted 3000. Elapsed 0/0 sec.
NOTICE:  Rel onek: Pages: 98 --> 25; Tuple(s) moved: 1000. Elapsed 0/1 sec.
NOTICE:  Index onek_stringu1: Pages 28; Tuples 1000: Deleted 1000. Elapsed 0/0 sec.
NOTICE:  Index onek_hundred: Pages 12; Tuples 1000: Deleted 1000. Elapsed 0/0 sec.
NOTICE:  Index onek_unique2: Pages 19; Tuples 1000: Deleted 1000. Elapsed 0/0 sec.
NOTICE:  Index onek_unique1: Pages 17; Tuples 1000: Deleted 1000. Elapsed 0/0 sec.
VACUUM
   </programlisting>
  </para>
 </refsect1>

 <refsect1 id="R1-SQL-VACUUM-3">
  <title>
   Compatibility
  </title>

  <refsect2 id="R2-SQL-VACUUM-4">
   <refsect2info>
    <date>1998-10-04</date>
   </refsect2info>
   <title>
    SQL92
   </title>
   <para>
    There is no <command>VACUUM</command> statement in <acronym>SQL92</acronym>.
   </para>
  </refsect2>
 </refsect1>
</refentry>

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