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><H1
><A
NAME="SQL-VACUUM"
></A
>VACUUM</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN79704"
></A
><H2
>Name</H2
>VACUUM -- garbage-collect and optionally analyze a database</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN79709"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>VACUUM [ ( { FULL | FREEZE | VERBOSE | ANALYZE } [, ...] ) ] [ <TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
> [ (<TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> [, ...] ) ] ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ <TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
> ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] ANALYZE [ <TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
> [ (<TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> [, ...] ) ] ]</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN79716"
></A
><H2
>Description</H2
><P
> <TT
CLASS="COMMAND"
>VACUUM</TT
> reclaims storage occupied by dead tuples.
In normal <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> operation, tuples that
are deleted or obsoleted by an update are not physically removed from
their table; they remain present until a <TT
CLASS="COMMAND"
>VACUUM</TT
> is
done. Therefore it's necessary to do <TT
CLASS="COMMAND"
>VACUUM</TT
>
periodically, especially on frequently-updated tables.
</P
><P
> With no parameter, <TT
CLASS="COMMAND"
>VACUUM</TT
> processes every table in the
current database that the current user has permission to vacuum.
With a parameter, <TT
CLASS="COMMAND"
>VACUUM</TT
> processes only that table.
</P
><P
> <TT
CLASS="COMMAND"
>VACUUM ANALYZE</TT
> performs a <TT
CLASS="COMMAND"
>VACUUM</TT
>
and then an <TT
CLASS="COMMAND"
>ANALYZE</TT
> for each selected table. This
is a handy combination form for routine maintenance scripts. See
<A
HREF="sql-analyze.html"
>ANALYZE</A
>
for more details about its processing.
</P
><P
> Plain <TT
CLASS="COMMAND"
>VACUUM</TT
> (without <TT
CLASS="LITERAL"
>FULL</TT
>) 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, as an exclusive lock
is not obtained. However, extra space is not returned to the operating
system (in most cases); it's just kept available for re-use within the
same table. <TT
CLASS="COMMAND"
>VACUUM FULL</TT
> rewrites the entire contents
of the table into a new disk file with no extra space, allowing unused
space to be returned to the operating system. This form is much slower and
requires an exclusive lock on each table while it is being processed.
</P
><P
> When the option list is surrounded by parentheses, the options can be
written in any order. Without parentheses, options must be specified
in exactly the order shown above.
The parenthesized syntax was added in
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 9.0; the unparenthesized
syntax is deprecated.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN79737"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>FULL</TT
></DT
><DD
><P
> Selects <SPAN
CLASS="QUOTE"
>"full"</SPAN
> vacuum, which can reclaim more
space, but takes much longer and exclusively locks the table.
This method also requires extra disk space, since it writes a
new copy of the table and doesn't release the old copy until
the operation is complete. Usually this should only be used when a
significant amount of space needs to be reclaimed from within the table.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>FREEZE</TT
></DT
><DD
><P
> Selects aggressive <SPAN
CLASS="QUOTE"
>"freezing"</SPAN
> of tuples.
Specifying <TT
CLASS="LITERAL"
>FREEZE</TT
> is equivalent to performing
<TT
CLASS="COMMAND"
>VACUUM</TT
> with the
<A
HREF="runtime-config-client.html#GUC-VACUUM-FREEZE-MIN-AGE"
>vacuum_freeze_min_age</A
> parameter
set to zero.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>VERBOSE</TT
></DT
><DD
><P
> Prints a detailed vacuum activity report for each table.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>ANALYZE</TT
></DT
><DD
><P
> Updates statistics used by the planner to determine the most
efficient way to execute a query.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
></DT
><DD
><P
> The name (optionally schema-qualified) of a specific table to
vacuum. Defaults to all tables in the current database.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
></DT
><DD
><P
> The name of a specific column to analyze. Defaults to all columns.
If a column list is specified, <TT
CLASS="LITERAL"
>ANALYZE</TT
> is implied.
</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN79776"
></A
><H2
>Outputs</H2
><P
> When <TT
CLASS="LITERAL"
>VERBOSE</TT
> is specified, <TT
CLASS="COMMAND"
>VACUUM</TT
> emits
progress messages to indicate which table is currently being
processed. Various statistics about the tables are printed as well.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN79781"
></A
><H2
>Notes</H2
><P
> To vacuum a table, one must ordinarily be the table's owner or a
superuser. However, database owners are allowed to
vacuum all tables in their databases, except shared catalogs.
(The restriction for shared catalogs means that a true database-wide
<TT
CLASS="COMMAND"
>VACUUM</TT
> can only be performed by a superuser.)
<TT
CLASS="COMMAND"
>VACUUM</TT
> will skip over any tables that the calling user
does not have permission to vacuum.
</P
><P
> <TT
CLASS="COMMAND"
>VACUUM</TT
> cannot be executed inside a transaction block.
</P
><P
> For tables with <ACRONYM
CLASS="ACRONYM"
>GIN</ACRONYM
> indexes, <TT
CLASS="COMMAND"
>VACUUM</TT
> (in
any form) also completes any pending index insertions, by moving pending
index entries to the appropriate places in the main <ACRONYM
CLASS="ACRONYM"
>GIN</ACRONYM
> index
structure. See <A
HREF="gin-implementation.html#GIN-FAST-UPDATE"
>Section 55.3.1</A
> for details.
</P
><P
> We recommend that active production databases be
vacuumed frequently (at least nightly), in order to
remove dead rows. After adding or deleting a large number
of rows, it might be a good idea to issue a <TT
CLASS="COMMAND"
>VACUUM
ANALYZE</TT
> command for the affected table. This will update the
system catalogs with
the results of all recent changes, and allow the
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> query planner to make better
choices in planning queries.
</P
><P
> The <TT
CLASS="OPTION"
>FULL</TT
> option is not recommended for routine use,
but might be useful in special cases. An example is when you have deleted
or updated most of the rows in a table and would like the table to
physically shrink to occupy less disk space and allow faster table
scans. <TT
CLASS="COMMAND"
>VACUUM FULL</TT
> will usually shrink the table
more than a plain <TT
CLASS="COMMAND"
>VACUUM</TT
> would.
</P
><P
> <TT
CLASS="COMMAND"
>VACUUM</TT
> causes a substantial increase in I/O traffic,
which might cause poor performance for other active sessions. Therefore,
it is sometimes advisable to use the cost-based vacuum delay feature.
See <A
HREF="runtime-config-resource.html#RUNTIME-CONFIG-RESOURCE-VACUUM-COST"
>Section 18.4.4</A
> for details.
</P
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> includes an <SPAN
CLASS="QUOTE"
>"autovacuum"</SPAN
>
facility which can automate routine vacuum maintenance. For more
information about automatic and manual vacuuming, see
<A
HREF="routine-vacuuming.html"
>Section 23.1</A
>.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN79807"
></A
><H2
>Examples</H2
><P
> To clean a single table <TT
CLASS="LITERAL"
>onek</TT
>, analyze it for
the optimizer and print a detailed vacuum activity report:
</P><PRE
CLASS="PROGRAMLISTING"
>VACUUM (VERBOSE, ANALYZE) onek;</PRE
><P></P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN79812"
></A
><H2
>Compatibility</H2
><P
> There is no <TT
CLASS="COMMAND"
>VACUUM</TT
> statement in the SQL standard.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN79816"
></A
><H2
>See Also</H2
><A
HREF="app-vacuumdb.html"
><SPAN
CLASS="APPLICATION"
>vacuumdb</SPAN
></A
>, <A
HREF="runtime-config-resource.html#RUNTIME-CONFIG-RESOURCE-VACUUM-COST"
>Section 18.4.4</A
>, <A
HREF="routine-vacuuming.html#AUTOVACUUM"
>Section 23.1.6</A
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