Current File : //opt/alt/postgresql11/usr/share/man/man7/VACUUM.7
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.\" Title: VACUUM
.\" Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\" Date: 2017-11-06
.\" Manual: PostgreSQL 9.2.24 Documentation
.\" Source: PostgreSQL 9.2.24
.\" Language: English
.\"
.TH "VACUUM" "7" "2017-11-06" "PostgreSQL 9.2.24" "PostgreSQL 9.2.24 Documentation"
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.SH "NAME"
VACUUM \- garbage\-collect and optionally analyze a database
.\" VACUUM
.SH "SYNOPSIS"
.sp
.nf
VACUUM [ ( { FULL | FREEZE | VERBOSE | ANALYZE } [, \&.\&.\&.] ) ] [ \fItable_name\fR [ (\fIcolumn_name\fR [, \&.\&.\&.] ) ] ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ \fItable_name\fR ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] ANALYZE [ \fItable_name\fR [ (\fIcolumn_name\fR [, \&.\&.\&.] ) ] ]
.fi
.SH "DESCRIPTION"
.PP
\fBVACUUM\fR
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
\fBVACUUM\fR
is done\&. Therefore it\*(Aqs necessary to do
\fBVACUUM\fR
periodically, especially on frequently\-updated tables\&.
.PP
With no parameter,
\fBVACUUM\fR
processes every table in the current database that the current user has permission to vacuum\&. With a parameter,
\fBVACUUM\fR
processes only that table\&.
.PP
\fBVACUUM ANALYZE\fR
performs a
\fBVACUUM\fR
and then an
\fBANALYZE\fR
for each selected table\&. This is a handy combination form for routine maintenance scripts\&. See
\fBANALYZE\fR(7)
for more details about its processing\&.
.PP
Plain
\fBVACUUM\fR
(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\*(Aqs just kept available for re\-use within the same table\&.
\fBVACUUM FULL\fR
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\&.
.PP
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\&.
.SH "PARAMETERS"
.PP
FULL
.RS 4
Selects
\(lqfull\(rq
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\*(Aqt 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\&.
.RE
.PP
FREEZE
.RS 4
Selects aggressive
\(lqfreezing\(rq
of tuples\&. Specifying
FREEZE
is equivalent to performing
\fBVACUUM\fR
with the
vacuum_freeze_min_age
parameter set to zero\&.
.RE
.PP
VERBOSE
.RS 4
Prints a detailed vacuum activity report for each table\&.
.RE
.PP
ANALYZE
.RS 4
Updates statistics used by the planner to determine the most efficient way to execute a query\&.
.RE
.PP
\fItable_name\fR
.RS 4
The name (optionally schema\-qualified) of a specific table to vacuum\&. Defaults to all tables in the current database\&.
.RE
.PP
\fIcolumn_name\fR
.RS 4
The name of a specific column to analyze\&. Defaults to all columns\&. If a column list is specified,
ANALYZE
is implied\&.
.RE
.SH "OUTPUTS"
.PP
When
VERBOSE
is specified,
\fBVACUUM\fR
emits progress messages to indicate which table is currently being processed\&. Various statistics about the tables are printed as well\&.
.SH "NOTES"
.PP
To vacuum a table, one must ordinarily be the table\*(Aqs 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
\fBVACUUM\fR
can only be performed by a superuser\&.)
\fBVACUUM\fR
will skip over any tables that the calling user does not have permission to vacuum\&.
.PP
\fBVACUUM\fR
cannot be executed inside a transaction block\&.
.PP
For tables with
GIN
indexes,
\fBVACUUM\fR
(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 55.3.1, \(lqGIN Fast Update Technique\(rq, in the documentation
for details\&.
.PP
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
\fBVACUUM ANALYZE\fR
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\&.
.PP
The
\fBFULL\fR
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\&.
\fBVACUUM FULL\fR
will usually shrink the table more than a plain
\fBVACUUM\fR
would\&.
.PP
\fBVACUUM\fR
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 18.4.4, \(lqCost-based Vacuum Delay\(rq, in the documentation
for details\&.
.PP
PostgreSQL
includes an
\(lqautovacuum\(rq
facility which can automate routine vacuum maintenance\&. For more information about automatic and manual vacuuming, see
Section 23.1, \(lqRoutine Vacuuming\(rq, in the documentation\&.
.SH "EXAMPLES"
.PP
To clean a single table
onek, analyze it for the optimizer and print a detailed vacuum activity report:
.sp
.if n \{\
.RS 4
.\}
.nf
VACUUM (VERBOSE, ANALYZE) onek;
.fi
.if n \{\
.RE
.\}
.SH "COMPATIBILITY"
.PP
There is no
\fBVACUUM\fR
statement in the SQL standard\&.
.SH "SEE ALSO"
\fBvacuumdb\fR(1), Section 18.4.4, \(lqCost-based Vacuum Delay\(rq, in the documentation, Section 23.1.6, \(lqThe Autovacuum Daemon\(rq, in the documentation
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