VACUUM(7)                                                 SQL Commands                                                 VACUUM(7)



NAME
       VACUUM - garbage-collect and optionally analyze a database


SYNOPSIS
       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  neces-
       sary 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  rou-
       tine maintenance scripts. See ANALYZE [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.  VACUUM  FULL  does  more
       extensive  processing, including moving of tuples across blocks to try to compact the table to the minimum number of disk
       blocks. This form is much slower and requires an exclusive lock on each table while it is being processed.

PARAMETERS
       FULL   Selects ``full'' vacuum, which can reclaim more space, but takes much longer and exclusively locks the table.

       FREEZE Selects aggressive ``freezing'' of tuples.  Specifying FREEZE is equivalent to performing  VACUUM  with  the  vac-
              uum_freeze_min_age parameter set to zero. The FREEZE option is deprecated and will be removed in a future release;
              set the parameter instead.

       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  data-
              base.

       column The name of a specific column to analyze. Defaults to all columns.

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  vac-
       uum  all tables in their databases, except shared catalogs.  (The restriction for shared catalogs means that a true data-
       base-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 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. The FULL option
       does not shrink indexes; a periodic REINDEX is still recommended. In fact, it is often faster to drop all indexes, VACUUM
       FULL, and recreate the indexes.

       VACUUM causes a substantial increase in I/O traffic, which might cause poor performance for other active sessions. There-
       fore, it is sometimes advisable to use the cost-based vacuum delay feature.  See 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 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 [vacuumdb(1)], in the documentation, in the documentation



SQL - Language Statements                                  2011-09-22                                                  VACUUM(7)