vacuum man page on BSDi

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VACUUM()			 SQL Commands			      VACUUM()

NAME
       VACUUM - Clean and analyze a Postgres database

SYNOPSIS
       VACUUM [ VERBOSE ] [ ANALYZE ] [ table ]
       VACUUM [ VERBOSE ] ANALYZE [ table [ (column [, ...] ) ] ]

   INPUTS
       VERBOSE
	      Prints a detailed vacuum activity report for each table.

       ANALYZE
	      Updates column statistics used by the optimizer to determine the
	      most efficient way to execute a query.

       table  The name of a specific table to vacuum. Defaults to all tables.

       column The name of a specific column to analyze. Defaults to  all  col‐
	      umns.

   OUTPUTS
       VACUUM The command has been accepted and the database is being cleaned.

       NOTICE: --Relation table--
	      The report header for table.

       NOTICE: Pages 98: Changed 25, Reapped 74, Empty 0, New 0;
	      The analysis for table itself.

       NOTICE: Index index: Pages 28;
	      The analysis for an index on the target table.

DESCRIPTION
       VACUUM serves two purposes in Postgres as both a means to reclaim stor‐
       age and also a means to collect information for the optimizer.

       VACUUM opens every table in  the	 database,  cleans  out	 records  from
       rolled  back  transactions,  and updates statistics in the system cata‐
       logs. The statistics maintained include the number of tuples and number
       of pages stored in all tables.

       VACUUM  ANALYZE	collects statistics representing the dispersion of the
       data in each column.  This information is valuable when	several	 query
       execution paths are possible.

       Running	VACUUM periodically will increase the speed of the database in
       processing user queries.

   NOTES
       The open database is the target for VACUUM.

       We recommend that active production databases be VACUUM-ed nightly,  in
       order to remove expired rows. After copying a large table into Postgres
       or after deleting a large number of records, it may be a good  idea  to
       issue a VACUUM ANALYZE query. This will update the system catalogs with
       the results of all recent changes, and allow the Postgres  query	 opti‐
       mizer to make better choices in planning user queries.

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

       regression=> vacuum verbose analyze onek;
       NOTICE:	--Relation onek--
       NOTICE:	Pages 98: Changed 25, Reapped 74, Empty 0, New 0;
		Tup 1000: Vac 3000, Crash 0, UnUsed 0, MinLen 188, MaxLen 188;
		Re-using: Free/Avail. Space 586952/586952; EndEmpty/Avail. Pages 0/74.
		Elapsed 0/0 sec.
       NOTICE:	Index onek_stringu1: Pages 28; Tuples 1000: Deleted 3000. Elapsed 0/0 sec.
       NOTICE:	Index onek_hundred: Pages 12; Tuples 1000: Deleted 3000. Elapsed 0/0 sec.
       NOTICE:	Index onek_unique2: Pages 19; Tuples 1000: Deleted 3000. Elapsed 0/0 sec.
       NOTICE:	Index onek_unique1: Pages 17; Tuples 1000: Deleted 3000. Elapsed 0/0 sec.
       NOTICE:	Rel onek: Pages: 98 --> 25; Tuple(s) moved: 1000. Elapsed 0/1 sec.
       NOTICE:	Index onek_stringu1: Pages 28; Tuples 1000: Deleted 1000. Elapsed 0/0 sec.
       NOTICE:	Index onek_hundred: Pages 12; Tuples 1000: Deleted 1000. Elapsed 0/0 sec.
       NOTICE:	Index onek_unique2: Pages 19; Tuples 1000: Deleted 1000. Elapsed 0/0 sec.
       NOTICE:	Index onek_unique1: Pages 17; Tuples 1000: Deleted 1000. Elapsed 0/0 sec.
       VACUUM

COMPATIBILITY
   SQL92
       There is no VACUUM statement in SQL92.

SQL - Language Statements	 29 March 2001			      VACUUM()
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