VACUUM(7) PostgreSQL 15.7 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 { AUTO | ON | OFF }
PROCESS_TOAST [ boolean ]
TRUNCATE [ boolean ]
PARALLEL integer
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. It also allows us to leverage multiple CPUs in order to
process indexes. This feature is known as parallel vacuum. To disable
this feature, one can use PARALLEL option and specify parallel workers
as zero. 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
Normally, VACUUM will skip index vacuuming when there are very few
dead tuples in the table. The cost of processing all of the table's
indexes is expected to greatly exceed the benefit of removing dead
index tuples when this happens. This option can be used to force
VACUUM to process indexes when there are more than zero dead
tuples. The default is AUTO, which allows VACUUM to skip index
vacuuming when appropriate. If INDEX_CLEANUP is set to ON, VACUUM
will conservatively remove all dead tuples from indexes. This may
be useful for backwards compatibility with earlier releases of
PostgreSQL where this was the standard behavior.
INDEX_CLEANUP can also be set to OFF to force VACUUM to always skip
index vacuuming, even when there are many dead tuples in the table.
This may be useful when it is necessary to make VACUUM run as
quickly as possible to avoid imminent transaction ID wraparound
(see Section 25.1.5). However, the wraparound failsafe mechanism
controlled by vacuum_failsafe_age will generally trigger
automatically to avoid transaction ID wraparound failure, and
should be preferred. 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 have no index and is
ignored if the FULL option is used. It also has no effect on the
transaction ID wraparound failsafe mechanism. When triggered it
will skip index vacuuming, even when INDEX_CLEANUP is set to ON.
PROCESS_TOAST
Specifies that VACUUM should attempt to process the corresponding
TOAST table for each relation, if one exists. This is usually the
desired behavior and is the default. Setting this option to false
may be useful when it is only necessary to vacuum the main
relation. This option is required when 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.
PARALLEL
Perform index vacuum and index cleanup phases of VACUUM in parallel
using integer background workers (for the details of each vacuum
phase, please refer to Table 28.41). The number of workers used to
perform the operation is equal to the number of indexes on the
relation that support parallel vacuum which is limited by the
number of workers specified with PARALLEL option if any which is
further limited by max_parallel_maintenance_workers. An index can
participate in parallel vacuum if and only if the size of the index
is more than min_parallel_index_scan_size. Please note that it is
not guaranteed that the number of parallel workers specified in
integer will be used during execution. It is possible for a vacuum
to run with fewer workers than specified, or even with no workers
at all. Only one worker can be used per index. So parallel workers
are launched only when there are at least 2 indexes in the table.
Workers for vacuum are launched before the start of each phase and
exit at the end of the phase. These behaviors might change in a
future release. This option can't be used with the FULL option.
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.
integer
Specifies a non-negative integer value passed to the selected
option.
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 70.4.1
for details.
We recommend that all databases be vacuumed regularly in order to
remove dead rows. PostgreSQL includes an “autovacuum” facility which
can automate routine vacuum maintenance. For more information about
automatic and manual vacuuming, see Section 25.1.
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.
The PARALLEL option is used only for vacuum purposes. If this option is
specified with the ANALYZE option, it does not affect ANALYZE.
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. For parallel
vacuum, each worker sleeps in proportion to the work done by that
worker. See Section 20.4.4 for details.
Each backend running VACUUM without the FULL option will report its
progress in the pg_stat_progress_vacuum view. Backends running VACUUM
FULL will instead report their progress in the pg_stat_progress_cluster
view. See Section 28.4.3 and Section 28.4.4 for details.
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 20.4.4, Section 25.1.6, Section 28.4.3,
Section 28.4.4
PostgreSQL 15.7 2024 VACUUM(7)
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