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ANALYZE(7)		PostgreSQL 9.6.3 Documentation		    ANALYZE(7)

NAME
       ANALYZE - collect statistics about a database

SYNOPSIS
       ANALYZE [ VERBOSE ] [ table_name	[ ( column_name	[, ...]	) ] ]

DESCRIPTION
       ANALYZE collects	statistics about the contents of tables	in the
       database, and stores the	results	in the pg_statistic system catalog.
       Subsequently, the query planner uses these statistics to	help determine
       the most	efficient execution plans for queries.

       With no parameter, ANALYZE examines every table in the current
       database. With a	parameter, ANALYZE examines only that table. It	is
       further possible	to give	a list of column names,	in which case only the
       statistics for those columns are	collected.

PARAMETERS
       VERBOSE
	   Enables display of progress messages.

       table_name
	   The name (possibly schema-qualified)	of a specific table to
	   analyze. If omitted,	all regular tables (but	not foreign tables) in
	   the current database	are analyzed.

       column_name
	   The name of a specific column to analyze. Defaults to all columns.

OUTPUTS
       When VERBOSE is specified, ANALYZE emits	progress messages to indicate
       which table is currently	being processed. Various statistics about the
       tables are printed as well.

NOTES
       Foreign tables are analyzed only	when explicitly	selected. Not all
       foreign data wrappers support ANALYZE. If the table's wrapper does not
       support ANALYZE,	the command prints a warning and does nothing.

       In the default PostgreSQL configuration,	the autovacuum daemon (see
       Section 24.1.6, "The Autovacuum Daemon",	in the documentation) takes
       care of automatic analyzing of tables when they are first loaded	with
       data, and as they change	throughout regular operation. When autovacuum
       is disabled, it is a good idea to run ANALYZE periodically, or just
       after making major changes in the contents of a table. Accurate
       statistics will help the	planner	to choose the most appropriate query
       plan, and thereby improve the speed of query processing.	A common
       strategy	for read-mostly	databases is to	run VACUUM(7) and ANALYZE once
       a day during a low-usage	time of	day. (This will	not be sufficient if
       there is	heavy update activity.)

       ANALYZE requires	only a read lock on the	target table, so it can	run in
       parallel	with other activity on the table.

       The statistics collected	by ANALYZE usually include a list of some of
       the most	common values in each column and a histogram showing the
       approximate data	distribution in	each column. One or both of these can
       be omitted if ANALYZE deems them	uninteresting (for example, in a
       unique-key column, there	are no common values) or if the	column data
       type does not support the appropriate operators.	There is more
       information about the statistics	in Chapter 24, Routine Database
       Maintenance Tasks, in the documentation.

       For large tables, ANALYZE takes a random	sample of the table contents,
       rather than examining every row.	This allows even very large tables to
       be analyzed in a	small amount of	time. Note, however, that the
       statistics are only approximate,	and will change	slightly each time
       ANALYZE is run, even if the actual table	contents did not change. This
       might result in small changes in	the planner's estimated	costs shown by
       EXPLAIN(7). In rare situations, this non-determinism will cause the
       planner's choices of query plans	to change after	ANALYZE	is run.	To
       avoid this, raise the amount of statistics collected by ANALYZE,	as
       described below.

       The extent of analysis can be controlled	by adjusting the
       default_statistics_target configuration variable, or on a
       column-by-column	basis by setting the per-column	statistics target with
       ALTER TABLE ... ALTER COLUMN ...	SET STATISTICS (see ALTER TABLE
       (ALTER_TABLE(7))). The target value sets	the maximum number of entries
       in the most-common-value	list and the maximum number of bins in the
       histogram. The default target value is 100, but this can	be adjusted up
       or down to trade	off accuracy of	planner	estimates against the time
       taken for ANALYZE and the amount	of space occupied in pg_statistic. In
       particular, setting the statistics target to zero disables collection
       of statistics for that column. It might be useful to do that for
       columns that are	never used as part of the WHERE, GROUP BY, or ORDER BY
       clauses of queries, since the planner will have no use for statistics
       on such columns.

       The largest statistics target among the columns being analyzed
       determines the number of	table rows sampled to prepare the statistics.
       Increasing the target causes a proportional increase in the time	and
       space needed to do ANALYZE.

       One of the values estimated by ANALYZE is the number of distinct	values
       that appear in each column. Because only	a subset of the	rows are
       examined, this estimate can sometimes be	quite inaccurate, even with
       the largest possible statistics target. If this inaccuracy leads	to bad
       query plans, a more accurate value can be determined manually and then
       installed with ALTER TABLE ... ALTER COLUMN ... SET (n_distinct = ...)
       (see ALTER TABLE	(ALTER_TABLE(7))).

       If the table being analyzed has one or more children, ANALYZE will
       gather statistics twice:	once on	the rows of the	parent table only, and
       a second	time on	the rows of the	parent table with all of its children.
       This second set of statistics is	needed when planning queries that
       traverse	the entire inheritance tree. The autovacuum daemon, however,
       will only consider inserts or updates on	the parent table itself	when
       deciding	whether	to trigger an automatic	analyze	for that table.	If
       that table is rarely inserted into or updated, the inheritance
       statistics will not be up to date unless	you run	ANALYZE	manually.

       If any of the child tables are foreign tables whose foreign data
       wrappers	do not support ANALYZE,	those child tables are ignored while
       gathering inheritance statistics.

       If the table being analyzed is completely empty,	ANALYZE	will not
       record new statistics for that table. Any existing statistics will be
       retained.

COMPATIBILITY
       There is	no ANALYZE statement in	the SQL	standard.

SEE ALSO
       VACUUM(7), vacuumdb(1), Section 19.4.4, "Cost-based Vacuum Delay", in
       the documentation, Section 24.1.6, "The Autovacuum Daemon", in the
       documentation

PostgreSQL 9.6.3		     2017			    ANALYZE(7)

NAME | SYNOPSIS | DESCRIPTION | PARAMETERS | OUTPUTS | NOTES | COMPATIBILITY | SEE ALSO

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