Provided by: postgresql-client-10_10.23-0ubuntu0.18.04.2_amd64 
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 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 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. If omitted, all regular tables
and materialized views in the current database are vacuumed. 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 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 64.4.1 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