VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ table ] VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] ANALYZE [ table [ (column [, ...] ) ] ] |
Selects "full" vacuum, which may reclaim more space, but takes much longer and exclusively locks the table.
Selects aggressive "freezing" of tuples.
Prints a detailed vacuum activity report for each table.
Updates statistics used by the optimizer to determine the most efficient way to execute a query.
The name of a specific table to vacuum. Defaults to all tables in the current database.
The name of a specific column to analyze. Defaults to all columns.
The command has been accepted and the database is being cleaned.
The report header for table.
The analysis for table itself.
The analysis for an index on the target table.
VACUUM reclaims storage occupied by deleted tuples. In normal PostgreSQL operation, tuples that are DELETEd or obsoleted by 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. 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.
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. VACUUM FULL does more extensive processing, including moving of tuples across blocks to try to compact the table to the minimum number of disk blocks. This form is much slower and requires an exclusive lock on each table while it is being processed.
FREEZE is a special-purpose option that causes tuples to be marked "frozen" as soon as possible, rather than waiting until they are quite old. If this is done when there are no other open transactions in the same database, then it is guaranteed that all tuples in the database are "frozen" and will not be subject to transaction ID wraparound problems, no matter how long the database is left un-vacuumed. FREEZE is not recommended for routine use. Its only intended usage is in connection with preparation of user-defined template databases, or other databases that are completely read-only and will not receive routine maintenance VACUUM operations. See the Administrator's Guide for details.
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 PostgreSQL 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 PostgreSQL query optimizer to make better choices in planning user queries.
The FULL option is not recommended for routine use, but may be useful in special cases. An example is when you have deleted most of the rows in a table and would like the table to physically shrink to occupy less disk space. VACUUM FULL will usually shrink the table more than a plain VACUUM would.
The following is an example from running VACUUM on a table in the regression database:
regression=> vacuum verbose analyze onek;
NOTICE: --Relation onek--
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. |