On Apache
Under GNU General Public License
2024-04-23 13:06 @3.129.13.201 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)
VACUUM(7) PostgreSQL 12.18 Documentation VACUUM(7)
NAME
VACUUM - garbage-collect and optionally analyze a database
SYNOPSIS
VACUUM [ ( option [, ...] ) ] [ table_and_columns [, ...] ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ table_and_columns [, ...] ]
where option can be one of:
FULL [ boolean ]
FREEZE [ boolean ]
VERBOSE [ boolean ]
ANALYZE [ boolean ]
DISABLE_PAGE_SKIPPING [ boolean ]
SKIP_LOCKED [ boolean ]
INDEX_CLEANUP [ boolean ]
TRUNCATE [ boolean ]
and table_and_columns is:
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.
Without a table_and_columns list, VACUUM processes every table and materialized view in
the current database that the current user has permission to vacuum. With a list, VACUUM
processes only those table(s).
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 ACCESS 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 when the contents
of the visibility map are suspect, which should happen only if there is a hardware or
software issue causing database corruption.
SKIP_LOCKED
Specifies that VACUUM should not wait for any conflicting locks to be released when
beginning work on a relation: if a relation cannot be locked immediately without
waiting, the relation is skipped. Note that even with this option, VACUUM may still
block when opening the relation's indexes. Additionally, VACUUM ANALYZE may still
block when acquiring sample rows from partitions, table inheritance children, and some
types of foreign tables. Also, while VACUUM ordinarily processes all partitions of
specified partitioned tables, this option will cause VACUUM to skip all partitions if
there is a conflicting lock on the partitioned table.
INDEX_CLEANUP
Specifies that VACUUM should attempt to remove index entries pointing to dead tuples.
This is normally the desired behavior and is the default unless the
vacuum_index_cleanup option has been set to false for the table to be vacuumed.
Setting this option to false may be useful when it is necessary to make vacuum run as
quickly as possible, for example to avoid imminent transaction ID wraparound (see
Section 24.1.5). However, if index cleanup is not performed regularly, performance may
suffer, because as the table is modified, indexes will accumulate dead tuples and the
table itself will accumulate dead line pointers that cannot be removed until index
cleanup is completed. This option has no effect for tables that do not have an index
and is ignored if the FULL option is used.
TRUNCATE
Specifies that VACUUM should attempt to truncate off any empty pages at the end of the
table and allow the disk space for the truncated pages to be returned to the operating
system. This is normally the desired behavior and is the default unless the
vacuum_truncate option has been set to false for the table to be vacuumed. Setting
this option to false may be useful to avoid ACCESS EXCLUSIVE lock on the table that
the truncation requires. This option is ignored if the FULL option is used.
boolean
Specifies whether the selected option should be turned on or off. You can write TRUE,
ON, or 1 to enable the option, and FALSE, OFF, or 0 to disable it. The boolean value
can also be omitted, in which case TRUE is assumed.
table_name
The name (optionally schema-qualified) of a specific table or materialized view to
vacuum. If the specified table is a partitioned table, all of its leaf partitions are
vacuumed.
column_name
The name of a specific column to analyze. Defaults to all columns. If a column list is
specified, ANALYZE must also be specified.
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 66.4.1 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 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.
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, Section 24.1.6
PostgreSQL 12.18 2024 VACUUM(7)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2024-04-23 13:06 @3.129.13.201 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)