1ANALYZE(7) PostgreSQL 13.4 Documentation ANALYZE(7)
2
6 ANALYZE - collect statistics about a database
7
9 ANALYZE [ ( option [, ...] ) ] [ table_and_columns [, ...] ]
10 ANALYZE [ VERBOSE ] [ table_and_columns [, ...] ]
11 where option can be one of:
13 VERBOSE [ boolean ]
15 SKIP_LOCKED [ boolean ]
16 and table_and_columns is:
18 table_name [ ( column_name [, ...] ) ]
20
22 ANALYZE collects statistics about the contents of tables in the
23 database, and stores the results in the pg_statistic system catalog.
24 Subsequently, the query planner uses these statistics to help determine
25 the most efficient execution plans for queries.
26 Without a table_and_columns list, ANALYZE processes every table and
28 materialized view in the current database that the current user has
29 permission to analyze. With a list, ANALYZE processes only those
30 table(s). It is further possible to give a list of column names for a
31 table, in which case only the statistics for those columns are
32 collected.
33 When the option list is surrounded by parentheses, the options can be
35 written in any order. The parenthesized syntax was added in PostgreSQL
36 11; the unparenthesized syntax is deprecated.
37
39 VERBOSE
40 Enables display of progress messages.
41 SKIP_LOCKED
43 Specifies that ANALYZE should not wait for any conflicting locks to
44 be released when beginning work on a relation: if a relation cannot
45 be locked immediately without waiting, the relation is skipped.
46 Note that even with this option, ANALYZE may still block when
47 opening the relation's indexes or when acquiring sample rows from
48 partitions, table inheritance children, and some types of foreign
49 tables. Also, while ANALYZE ordinarily processes all partitions of
50 specified partitioned tables, this option will cause ANALYZE to
51 skip all partitions if there is a conflicting lock on the
52 partitioned table.
53 boolean
55 Specifies whether the selected option should be turned on or off.
56 You can write TRUE, ON, or 1 to enable the option, and FALSE, OFF,
57 or 0 to disable it. The boolean value can also be omitted, in which
58 case TRUE is assumed.
59 table_name
61 The name (possibly schema-qualified) of a specific table to
62 analyze. If omitted, all regular tables, partitioned tables, and
63 materialized views in the current database are analyzed (but not
64 foreign tables). If the specified table is a partitioned table,
65 both the inheritance statistics of the partitioned table as a whole
66 and statistics of the individual partitions are updated.
67 column_name
69 The name of a specific column to analyze. Defaults to all columns.
70
72 When VERBOSE is specified, ANALYZE emits progress messages to indicate
73 which table is currently being processed. Various statistics about the
74 tables are printed as well.
75
77 To analyze a table, one must ordinarily be the table's owner or a
78 superuser. However, database owners are allowed to analyze all tables
79 in their databases, except shared catalogs. (The restriction for shared
80 catalogs means that a true database-wide ANALYZE can only be performed
81 by a superuser.) ANALYZE will skip over any tables that the calling
82 user does not have permission to analyze.
83 Foreign tables are analyzed only when explicitly selected. Not all
85 foreign data wrappers support ANALYZE. If the table's wrapper does not
86 support ANALYZE, the command prints a warning and does nothing.
87 In the default PostgreSQL configuration, the autovacuum daemon (see
89 Section 24.1.6) takes care of automatic analyzing of tables when they
90 are first loaded with data, and as they change throughout regular
91 operation. When autovacuum is disabled, it is a good idea to run
92 ANALYZE periodically, or just after making major changes in the
93 contents of a table. Accurate statistics will help the planner to
94 choose the most appropriate query plan, and thereby improve the speed
95 of query processing. A common strategy for read-mostly databases is to
96 run VACUUM(7) and ANALYZE once a day during a low-usage time of day.
97 (This will not be sufficient if there is heavy update activity.)
98 ANALYZE requires only a read lock on the target table, so it can run in
100 parallel with other activity on the table.
101 The statistics collected by ANALYZE usually include a list of some of
103 the most common values in each column and a histogram showing the
104 approximate data distribution in each column. One or both of these can
105 be omitted if ANALYZE deems them uninteresting (for example, in a
106 unique-key column, there are no common values) or if the column data
107 type does not support the appropriate operators. There is more
108 information about the statistics in Chapter 24.
109 For large tables, ANALYZE takes a random sample of the table contents,
111 rather than examining every row. This allows even very large tables to
112 be analyzed in a small amount of time. Note, however, that the
113 statistics are only approximate, and will change slightly each time
114 ANALYZE is run, even if the actual table contents did not change. This
115 might result in small changes in the planner's estimated costs shown by
116 EXPLAIN(7). In rare situations, this non-determinism will cause the
117 planner's choices of query plans to change after ANALYZE is run. To
118 avoid this, raise the amount of statistics collected by ANALYZE, as
119 described below.
120 The extent of analysis can be controlled by adjusting the
122 default_statistics_target configuration variable, or on a
123 column-by-column basis by setting the per-column statistics target with
124 ALTER TABLE ... ALTER COLUMN ... SET STATISTICS (see ALTER TABLE
125 (ALTER_TABLE(7))). The target value sets the maximum number of entries
126 in the most-common-value list and the maximum number of bins in the
127 histogram. The default target value is 100, but this can be adjusted up
128 or down to trade off accuracy of planner estimates against the time
129 taken for ANALYZE and the amount of space occupied in pg_statistic. In
130 particular, setting the statistics target to zero disables collection
131 of statistics for that column. It might be useful to do that for
132 columns that are never used as part of the WHERE, GROUP BY, or ORDER BY
133 clauses of queries, since the planner will have no use for statistics
134 on such columns.
135 The largest statistics target among the columns being analyzed
137 determines the number of table rows sampled to prepare the statistics.
138 Increasing the target causes a proportional increase in the time and
139 space needed to do ANALYZE.
140 One of the values estimated by ANALYZE is the number of distinct values
142 that appear in each column. Because only a subset of the rows are
143 examined, this estimate can sometimes be quite inaccurate, even with
144 the largest possible statistics target. If this inaccuracy leads to bad
145 query plans, a more accurate value can be determined manually and then
146 installed with ALTER TABLE ... ALTER COLUMN ... SET (n_distinct = ...)
147 (see ALTER TABLE (ALTER_TABLE(7))).
148 If the table being analyzed has one or more children, ANALYZE will
150 gather statistics twice: once on the rows of the parent table only, and
151 a second time on the rows of the parent table with all of its children.
152 This second set of statistics is needed when planning queries that
153 traverse the entire inheritance tree. The autovacuum daemon, however,
154 will only consider inserts or updates on the parent table itself when
155 deciding whether to trigger an automatic analyze for that table. If
156 that table is rarely inserted into or updated, the inheritance
157 statistics will not be up to date unless you run ANALYZE manually.
158 If any of the child tables are foreign tables whose foreign data
160 wrappers do not support ANALYZE, those child tables are ignored while
161 gathering inheritance statistics.
162 If the table being analyzed is completely empty, ANALYZE will not
164 record new statistics for that table. Any existing statistics will be
165 retained.
166
168 There is no ANALYZE statement in the SQL standard.
169
171 VACUUM(7), vacuumdb(1), Section 19.4.4, Section 24.1.6
172PostgreSQL 13.4 2021 ANALYZE(7)