Provided by: postgresql-client-9.1_9.1.3-2_amd64 bug

NAME

       VACUUM - garbage-collect and optionally analyze a database

SYNOPSIS

       VACUUM [ ( { FULL | FREEZE | VERBOSE | ANALYZE } [, ...] ) ] [ table [ (column [, ...] ) ] ]
       VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ table ]
       VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] ANALYZE [ table [ (column [, ...] ) ] ]

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 parameter set to zero.

       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.

       table
           The name (optionally schema-qualified) of a specific table to vacuum. Defaults to all
           tables in the current database.

       column
           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 54.3.1, “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 18.4.3, “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 23.1,
       “Routine Vacuuming”, in the documentation.

EXAMPLES

       The following is an example from running VACUUM on a table in the regression database:

           regression=# VACUUM (VERBOSE, ANALYZE) onek;
           INFO:  vacuuming "public.onek"
           INFO:  index "onek_unique1" now contains 1000 tuples in 14 pages
           DETAIL:  3000 index tuples were removed.
           0 index pages have been deleted, 0 are currently reusable.
           CPU 0.01s/0.08u sec elapsed 0.18 sec.
           INFO:  index "onek_unique2" now contains 1000 tuples in 16 pages
           DETAIL:  3000 index tuples were removed.
           0 index pages have been deleted, 0 are currently reusable.
           CPU 0.00s/0.07u sec elapsed 0.23 sec.
           INFO:  index "onek_hundred" now contains 1000 tuples in 13 pages
           DETAIL:  3000 index tuples were removed.
           0 index pages have been deleted, 0 are currently reusable.
           CPU 0.01s/0.08u sec elapsed 0.17 sec.
           INFO:  index "onek_stringu1" now contains 1000 tuples in 48 pages
           DETAIL:  3000 index tuples were removed.
           0 index pages have been deleted, 0 are currently reusable.
           CPU 0.01s/0.09u sec elapsed 0.59 sec.
           INFO:  "onek": removed 3000 tuples in 108 pages
           DETAIL:  CPU 0.01s/0.06u sec elapsed 0.07 sec.
           INFO:  "onek": found 3000 removable, 1000 nonremovable tuples in 143 pages
           DETAIL:  0 dead tuples cannot be removed yet.
           There were 0 unused item pointers.
           0 pages are entirely empty.
           CPU 0.07s/0.39u sec elapsed 1.56 sec.
           INFO:  analyzing "public.onek"
           INFO:  "onek": 36 pages, 1000 rows sampled, 1000 estimated total rows
           VACUUM

COMPATIBILITY

       There is no VACUUM statement in the SQL standard.

SEE ALSO

       vacuumdb(1), Section 18.4.3, “Cost-based Vacuum Delay”, in the documentation, Section
       23.1.5, “The Autovacuum Daemon”, in the documentation