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VACUUM(7)		PostgreSQL 9.6.3 Documentation		     VACUUM(7)

NAME
       VACUUM -	garbage-collect	and optionally analyze a database

SYNOPSIS
       VACUUM [	( { FULL | FREEZE | VERBOSE | ANALYZE |	DISABLE_PAGE_SKIPPING }	[, ...]	) ] [ table_name [ (column_name	[, ...]	) ] ]
       VACUUM [	FULL ] [ FREEZE	] [ VERBOSE ] [	table_name ]
       VACUUM [	FULL ] [ FREEZE	] [ VERBOSE ] ANALYZE [	table_name [ (column_name [, ...] ) ] ]

DESCRIPTION
       VACUUM reclaims storage occupied	by dead	tuples.	In normal PostgreSQL
       operation, tuples that are deleted or obsoleted by an update are	not
       physically removed from their table; they remain	present	until a	VACUUM
       is done.	Therefore it's necessary to do VACUUM periodically, especially
       on frequently-updated tables.

       With no parameter, VACUUM processes every table in the current database
       that the	current	user has permission to vacuum. With a parameter,
       VACUUM processes	only that table.

       VACUUM ANALYZE performs a VACUUM	and then an ANALYZE for	each selected
       table. This is a	handy combination form for routine maintenance
       scripts.	See ANALYZE(7) for more	details	about its processing.

       Plain VACUUM (without FULL) 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.  VACUUM FULL	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.

       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
       PostgreSQL 9.0; the unparenthesized syntax is deprecated.

PARAMETERS
       FULL
	   Selects "full" 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.

       FREEZE
	   Selects aggressive "freezing" of tuples. Specifying FREEZE is
	   equivalent to performing VACUUM with	the vacuum_freeze_min_age and
	   vacuum_freeze_table_age parameters set to zero. Aggressive freezing
	   is always performed when the	table is rewritten, so this option is
	   redundant when FULL is specified.

       VERBOSE
	   Prints a detailed vacuum activity report for	each table.

       ANALYZE
	   Updates statistics used by the planner to determine the most
	   efficient way to execute a query.

       DISABLE_PAGE_SKIPPING
	   Normally, VACUUM will skip pages based on the visibility map. Pages
	   where all tuples are	known to be frozen can always be skipped, and
	   those where all tuples are known to be visible to all transactions
	   may be skipped except when performing an aggressive vacuum.
	   Furthermore,	except when performing an aggressive vacuum, some
	   pages may be	skipped	in order to avoid waiting for other sessions
	   to finish using them. This option disables all page-skipping
	   behavior, and is intended to	be used	only the contents of the
	   visibility map are thought to be suspect, which should happen only
	   if there is a hardware or software issue causing database
	   corruption.

       table_name
	   The name (optionally	schema-qualified) of a specific	table to
	   vacuum. Defaults to all tables in the current database.

       column_name
	   The name of a specific column to analyze. Defaults to all columns.
	   If a	column list is specified, ANALYZE is implied.

OUTPUTS
       When VERBOSE is specified, VACUUM emits progress	messages to indicate
       which table is currently	being processed. Various statistics about the
       tables are printed as well.

NOTES
       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	VACUUM can only	be performed
       by a superuser.)	 VACUUM	will skip over any tables that the calling
       user does not have permission to	vacuum.

       VACUUM cannot be	executed inside	a transaction block.

       For tables with GIN indexes, VACUUM (in any form) also completes	any
       pending index insertions, by moving pending index entries to the
       appropriate places in the main GIN index	structure. See Section 63.4.1,
       "GIN Fast Update	Technique", in the documentation for details.

       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
       VACUUM ANALYZE command for the affected table. This will	update the
       system catalogs with the	results	of all recent changes, and allow the
       PostgreSQL query	planner	to make	better choices in planning queries.

       The FULL	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.  VACUUM FULL will
       usually shrink the table	more than a plain VACUUM would.

       VACUUM 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 Section
       19.4.4, "Cost-based Vacuum Delay", in the documentation for details.

       PostgreSQL includes an "autovacuum" facility which can automate routine
       vacuum maintenance. For more information	about automatic	and manual
       vacuuming, see Section 24.1, "Routine Vacuuming", in the	documentation.

EXAMPLES
       To clean	a single table onek, analyze it	for the	optimizer and print a
       detailed	vacuum activity	report:

	   VACUUM (VERBOSE, ANALYZE) onek;

COMPATIBILITY
       There is	no VACUUM statement in the SQL standard.

SEE ALSO
       vacuumdb(1), Section 19.4.4, "Cost-based	Vacuum Delay", in the
       documentation, Section 24.1.6, "The Autovacuum Daemon", in the
       documentation

PostgreSQL 9.6.3		     2017			     VACUUM(7)

NAME | SYNOPSIS | DESCRIPTION | PARAMETERS | OUTPUTS | NOTES | EXAMPLES | COMPATIBILITY | SEE ALSO

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