VACUUM
SQL - Language Statements
VACUUM
Clean and analyze a Postgres database
1999-07-20
VACUUM [ VERBOSE ] [ ANALYZE ] [ table ]
VACUUM [ VERBOSE ] ANALYZE [ table [ (column [, ...] ) ] ]
1998-10-04
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.
1998-10-04
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;
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.
The analysis for table itself.
NOTICE: Index index: Pages 28;
Tuples 1000: Deleted 3000. Elapsed 0/0 sec.
The analysis for an index on the target table.
1998-10-04
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 class in the database,
cleans out records from rolled back transactions, and updates statistics in the
system catalogs. The statistics maintained include the number of
tuples and number of pages stored in all classes.
VACUUM ANALYZE collects statistics representing the
disbursion 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.
1998-10-04
Notes
The open database is the target for VACUUM.
We recommend that active production databases be
VACUUMM-ed nightly, in order to keep remove
expired rows. After copying a large class 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 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
1998-10-04
SQL92
There is no VACUUM statement in SQL92.