VACUUM — garbage-collect and optionally analyze a database
VACUUM [ (option[, ...] ) ] [table_and_columns[, ...] ] VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [table_and_columns[, ...] ] whereoptioncan be one of: FULL FREEZE VERBOSE ANALYZE DISABLE_PAGE_SKIPPING andtable_and_columnsis:table_name[ (column_name[, ...] ) ]
VACUUM 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.
Without a table_and_columns
list, VACUUM processes every table and materialized view
in the current database that the current user has permission to vacuum.
With a list, VACUUM processes only those table(s).
VACUUM ANALYZE performs a VACUUM
and then an ANALYZE for each selected table. This
is a handy combination form for routine maintenance scripts. See
ANALYZE
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 ACCESS 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.
FULLSelects “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
vacuum_freeze_min_age and
vacuum_freeze_table_age parameters
set to zero. Aggressive freezing is always performed when the
table is rewritten, so this option is redundant when FULL
is specified.
VERBOSEPrints a detailed vacuum activity report for each table.
ANALYZEUpdates statistics used by the planner to determine the most efficient way to execute a query.
DISABLE_PAGE_SKIPPING
Normally, VACUUM will skip pages based on the visibility map. Pages where
all tuples are known to be frozen can always be skipped, and those
where all tuples are known to be visible to all transactions may be
skipped except when performing an aggressive vacuum. Furthermore,
except when performing an aggressive vacuum, some pages may be skipped
in order to avoid waiting for other sessions to finish using them.
This option disables all page-skipping behavior, and is intended to
be used only when the contents of the visibility map are
suspect, which should happen only if there is a hardware or software
issue causing database corruption.
table_nameThe name (optionally schema-qualified) of a specific table or materialized view to vacuum. If the specified table is a partitioned table, all of its leaf partitions are vacuumed.
column_name
The name of a specific column to analyze. Defaults to all columns.
If a column list is specified, ANALYZE must also be
specified.
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.
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 Section 66.4.1 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 FULL 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 Section 19.4.4 for details.
PostgreSQL includes an “autovacuum” facility which can automate routine vacuum maintenance. For more information about automatic and manual vacuuming, see Section 24.1.
To clean a single table onek, analyze it for
the optimizer and print a detailed vacuum activity report:
VACUUM (VERBOSE, ANALYZE) onek;
There is no VACUUM statement in the SQL standard.