|
Hopefully, this page is exactly what you are looking for, but if not, you can always find further assistance on Unix/Linux Forum!
SQL Commands VACUUM()
NAME
VACUUM - garbage-collect and optionally analyze a database
SYNOPSIS
VACUUM [ FULL | FREEZE ] [ VERBOSE ] [ table ]
VACUUM [ FULL | FREEZE ] [ VERBOSE ] ANALYZE [ table [ (column [, ...] ) ] ]
DESCRIPTION
VACUUM reclaims storage occupied by deleted tuples. In nor-
mal 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. 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 ANALYZE [analyze(5)] 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. 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 prob-
lems, no matter how long the database is left unvacuumed.
FREEZE is not recommended for routine use. Its only intended
usage is in connection with preparation of user-defined tem-
plate databases, or other databases that are completely
read-only and will not receive routine maintenance VACUUM
operations. See the documentation for details.
PARAMETERS
FULL Selects ``full'' vacuum, which may reclaim more space,
but takes much longer and exclusively locks the table.
SQL - Language StatemLast change: 2005-11-05 1
SQL Commands VACUUM()
FREEZE
Selects aggressive ``freezing'' of tuples.
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.
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
We recommend that active production databases be vacuumed
frequently (at least nightly), in order to remove expired
rows. After adding or deleting a large number of rows, it
may 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 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.
VACUUM causes a substantial increase in I/O traffic, which
can cause poor performance for other active sessions. There-
fore, it is sometimes advisable to use the cost-based vacuum
delay feature. See the documentation for details.
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"
SQL - Language StatemLast change: 2005-11-05 2
SQL Commands VACUUM()
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
vacuumdb [vacuumdb(1)], the documentation
SQL - Language StatemLast change: 2005-11-05 3
Man(1) output converted with
man2html and wrapped by fishsponge
This page was generated on Wed Sep 12 11:28:01 GMT 2007
|
Your favourite pages:
No pages logged yet.
Trying to save cookie... Top 10 most popular pages:
sqlite3 man page (5334 hits)
(openSUSE 10.2)
svn man page (5208 hits)
(FreeBSD 6.2)
adv_cap_autoneg man page (4870 hits)
(Solaris 10 11_06)
CPAN man page (4607 hits)
(Suse Linux 10.1)
ssh man page (4342 hits)
(Suse Linux 10.1)
ssh-socks5-proxy-connect man page (2876 hits)
(Solaris 10 11_06)
netcat man page (2717 hits)
(Suse Linux 10.1)
pprosetup man page (2487 hits)
(Solaris 10 11_06)
startproc man page (2471 hits)
(Suse Linux 10.1)
signal man page (2407 hits)
(Suse Linux 10.1)
|
Man Pages 
