Index Index for
Section 5
Index Alphabetical
listing for V
Bottom of page Bottom of
page		 

VACUUM()


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 deleted 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.
  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 [analyze(5)] 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 may 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 vacuum_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 database.

  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

  VACUUM cannot be executed inside a transaction block.

  We recommend that active production databases be vacuumed frequently (at
  least nightly), in order to remove expired rows. After adding or deleting a
  large number of rows, it may 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 may be useful in
  special cases. An example is when you have deleted most of the rows in a
  table and would like the table to physically shrink to occupy less disk
  space. 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 can cause poor
  performance for other active sessions. Therefore, 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

Index Index for
Section 5
Index Alphabetical
listing for V
Top of page Top of
page