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

       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 23.1.6, “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 23, 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 18.4.4, “Cost-based Vacuum Delay”, in the documentation, Section 23.1.6,
       “The Autovacuum Daemon”, in the documentation

PostgreSQL 9.5.25                                     2021                                            ANALYZE(7)