VACUUM7SQL - Language StatementsVACUUMgarbage-collect and optionally analyze a databaseVACUUM
VACUUM [ ( { FULL | FREEZE | VERBOSE | ANALYZE } [, ...] ) ] [ table [ (column [, ...] ) ] ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ table ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] ANALYZE [ table [ (column [, ...] ) ] ]
DescriptionVACUUM reclaims storage occupied by dead 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 that the current user has permission to vacuum.
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
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. However, extra space is not returned to the operating
system (in most cases); it's just kept available for re-use within the
same table. VACUUM FULL rewrites the entire contents
of the table into a new disk file with no extra space, allowing unused
space to be returned to the operating system. This form is much slower and
requires an exclusive lock on each table while it is being processed.
When the option list is surrounded by parentheses, the options can be
written in any order. Without parentheses, options must be specified
in exactly the order shown above.
The parenthesized syntax was added in
PostgreSQL 9.0; the unparenthesized
syntax is deprecated.
ParametersFULL
Selects full vacuum, which can reclaim more
space, but takes much longer and exclusively locks the table.
This method also requires extra disk space, since it writes a
new copy of the table and doesn't release the old copy until
the operation is complete. Usually this should only be used when a
significant amount of space needs to be reclaimed from within the table.
FREEZE
Selects aggressive freezing of tuples.
Specifying FREEZE is equivalent to performing
VACUUM with the
parameter
set to zero.
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.
If a column list is specified, ANALYZE> is implied.
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
To vacuum a table, one must ordinarily be the table's owner or a
superuser. However, database owners are allowed to
vacuum all tables in their databases, except shared catalogs.
(The restriction for shared catalogs means that a true database-wide
VACUUM> can only be performed by a superuser.)
VACUUM> will skip over any tables that the calling user
does not have permission to vacuum.
VACUUM> cannot be executed inside a transaction block.
For tables with GIN> indexes, VACUUM (in
any form) also completes any pending index insertions, by moving pending
index entries to the appropriate places in the main GIN> index
structure. See for details.
We recommend that active production databases be
vacuumed frequently (at least nightly), in order to
remove dead rows. After adding or deleting a large number
of rows, it might 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 option is not recommended for routine use,
but might be useful in special cases. An example is when you have deleted
or updated most of the rows in a table and would like the table to
physically shrink to occupy less disk space and allow faster table
scans. VACUUM FULL will usually shrink the table
more than a plain VACUUM would.
VACUUM causes a substantial increase in I/O traffic,
which might cause poor performance for other active sessions. Therefore,
it is sometimes advisable to use the cost-based vacuum delay feature.
See for details.
PostgreSQL includes an autovacuum>
facility which can automate routine vacuum maintenance. For more
information about automatic and manual vacuuming, see
.
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