VACUUM(7) PostgreSQL 9.6.6 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 9.6.6 2017 VACUUM(7)
PostgreSQL 9.6.6 - Generated Sat Dec 2 13:32:01 CST 2017