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 columns.

   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 storage 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 statis­
       tics  in  the  system  catalogs. The statistics maintained
       include the number of tuples and number of pages stored in
       all tables.

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

       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  ANA­
       LYZE  query. This will update the system catalogs with the
       results of all recent  changes,  and  allow  the  Postgres
       query  optimizer  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.


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