ANALYZE(7) PostgreSQL 15.7 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 15.7 2024 ANALYZE(7)
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