On Apache
Under GNU General Public License
2025-11-22 19:21 @216.73.216.63 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)
ANALYZE(7) PostgreSQL 14.19 Documentation ANALYZE(7)
NAME
ANALYZE - collect statistics about a database
SYNOPSIS
ANALYZE [ ( option [, ...] ) ] [ table_and_columns [, ...] ]
ANALYZE [ VERBOSE ] [ table_and_columns [, ...] ]
where option can be one of:
VERBOSE [ boolean ]
SKIP_LOCKED [ boolean ]
and table_and_columns is:
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.
Without a table_and_columns list, ANALYZE processes every table and materialized view in
the current database that the current user has permission to analyze. With a list, ANALYZE
processes only those table(s). It is further possible to give a list of column names for a
table, in which case only the statistics for those columns are collected.
When the option list is surrounded by parentheses, the options can be written in any
order. The parenthesized syntax was added in PostgreSQL 11; the unparenthesized syntax is
deprecated.
PARAMETERS
VERBOSE
Enables display of progress messages.
SKIP_LOCKED
Specifies that ANALYZE should not wait for any conflicting locks to be released when
beginning work on a relation: if a relation cannot be locked immediately without
waiting, the relation is skipped. Note that even with this option, ANALYZE may still
block when opening the relation's indexes or when acquiring sample rows from
partitions, table inheritance children, and some types of foreign tables. Also, while
ANALYZE ordinarily processes all partitions of specified partitioned tables, this
option will cause ANALYZE to skip all partitions if there is a conflicting lock on the
partitioned table.
boolean
Specifies whether the selected option should be turned on or off. You can write TRUE,
ON, or 1 to enable the option, and FALSE, OFF, or 0 to disable it. The boolean value
can also be omitted, in which case TRUE is assumed.
table_name
The name (possibly schema-qualified) of a specific table to analyze. If omitted, all
regular tables, partitioned tables, and materialized views in the current database are
analyzed (but not foreign tables). If the specified table is a partitioned table, both
the inheritance statistics of the partitioned table as a whole and statistics of the
individual partitions are updated.
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
To analyze a table, one must ordinarily be the table's owner or a superuser. However,
database owners are allowed to analyze all tables in their databases, except shared
catalogs. (The restriction for shared catalogs means that a true database-wide ANALYZE can
only be performed by a superuser.) ANALYZE will skip over any tables that the calling
user does not have permission to analyze.
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 25.1.6) 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 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 25.
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. 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. 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 = ...).
If the table being analyzed has inheritance children, ANALYZE gathers two sets of
statistics: one on the rows of the parent table only, and a second including rows of both
the parent table and all of its children. This second set of statistics is needed when
planning queries that process the inheritance tree as a whole. The child tables themselves
are not individually analyzed in this case. 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.
For partitioned tables, ANALYZE gathers statistics by sampling rows from all partitions;
in addition, it will recurse into each partition and update its statistics. Each leaf
partition is analyzed only once, even with multi-level partitioning. No statistics are
collected for only the parent table (without data from its partitions), because with
partitioning it's guaranteed to be empty.
The autovacuum daemon does not process partitioned tables, nor does it process inheritance
parents if only the children are ever modified. It is usually necessary to periodically
run a manual ANALYZE to keep the statistics of the table hierarchy up to date.
If any child tables or partitions are foreign tables whose foreign data wrappers do not
support ANALYZE, those 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.
Each backend running ANALYZE will report its progress in the pg_stat_progress_analyze
view. See Section 28.4.1 for details.
COMPATIBILITY
There is no ANALYZE statement in the SQL standard.
SEE ALSO
VACUUM(7), vacuumdb(1), Section 20.4.4, Section 25.1.6, Section 28.4.1
PostgreSQL 14.19 2025 ANALYZE(7)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2025-11-22 19:21 @216.73.216.63 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)