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()
