VACUUM

VACUUM

7

SQL - Language Statements

VACUUM

garbage-collect and optionally analyze a database

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 [???](#sql-analyze) 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
    [???](#guc-vacuum-freeze-min-age) and
    [???](#guc-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](#vacuum-for-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 [???](#vacuum-for-wraparound)). However, the
    wraparound failsafe mechanism controlled by
    [???](#guc-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 [???](#vacuum-phases)). 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
    [???](#guc-max-parallel-maintenance-workers). An index can
    participate in parallel vacuum if and only if the size of the index
    is more than [???](#guc-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
[???](#gin-fast-update) 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.

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 [???](#runtime-config-resource-vacuum-cost) for details.

PostgreSQL includes an "autovacuum" facility which can automate routine
vacuum maintenance. For more information about automatic and manual
vacuuming, see [???](#routine-vacuuming).

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 [???](#vacuum-progress-reporting)
and [???](#cluster-progress-reporting) 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
========
