1ANALYZE(7)               PostgreSQL 10.7 Documentation              ANALYZE(7)
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NAME

6       ANALYZE - collect statistics about a database
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SYNOPSIS

9       ANALYZE [ VERBOSE ] [ table_name [ ( column_name [, ...] ) ] ]
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DESCRIPTION

12       ANALYZE collects statistics about the contents of tables in the
13       database, and stores the results in the pg_statistic system catalog.
14       Subsequently, the query planner uses these statistics to help determine
15       the most efficient execution plans for queries.
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17       With no parameter, ANALYZE examines every table in the current
18       database. With a parameter, ANALYZE examines only that table. It is
19       further possible to give a list of column names, in which case only the
20       statistics for those columns are collected.
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PARAMETERS

23       VERBOSE
24           Enables display of progress messages.
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26       table_name
27           The name (possibly schema-qualified) of a specific table to
28           analyze. If omitted, all regular tables, partitioned tables, and
29           materialized views in the current database are analyzed (but not
30           foreign tables). If the specified table is a partitioned table,
31           both the inheritance statistics of the partitioned table as a whole
32           and statistics of the individual partitions are updated.
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34       column_name
35           The name of a specific column to analyze. Defaults to all columns.
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OUTPUTS

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

43       Foreign tables are analyzed only when explicitly selected. Not all
44       foreign data wrappers support ANALYZE. If the table's wrapper does not
45       support ANALYZE, the command prints a warning and does nothing.
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47       In the default PostgreSQL configuration, the autovacuum daemon (see
48       Section 24.1.6) takes care of automatic analyzing of tables when they
49       are first loaded with data, and as they change throughout regular
50       operation. When autovacuum is disabled, it is a good idea to run
51       ANALYZE periodically, or just after making major changes in the
52       contents of a table. Accurate statistics will help the planner to
53       choose the most appropriate query plan, and thereby improve the speed
54       of query processing. A common strategy for read-mostly databases is to
55       run VACUUM(7) and ANALYZE once a day during a low-usage time of day.
56       (This will not be sufficient if there is heavy update activity.)
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58       ANALYZE requires only a read lock on the target table, so it can run in
59       parallel with other activity on the table.
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61       The statistics collected by ANALYZE usually include a list of some of
62       the most common values in each column and a histogram showing the
63       approximate data distribution in each column. One or both of these can
64       be omitted if ANALYZE deems them uninteresting (for example, in a
65       unique-key column, there are no common values) or if the column data
66       type does not support the appropriate operators. There is more
67       information about the statistics in Chapter 24.
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69       For large tables, ANALYZE takes a random sample of the table contents,
70       rather than examining every row. This allows even very large tables to
71       be analyzed in a small amount of time. Note, however, that the
72       statistics are only approximate, and will change slightly each time
73       ANALYZE is run, even if the actual table contents did not change. This
74       might result in small changes in the planner's estimated costs shown by
75       EXPLAIN(7). In rare situations, this non-determinism will cause the
76       planner's choices of query plans to change after ANALYZE is run. To
77       avoid this, raise the amount of statistics collected by ANALYZE, as
78       described below.
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80       The extent of analysis can be controlled by adjusting the
81       default_statistics_target configuration variable, or on a
82       column-by-column basis by setting the per-column statistics target with
83       ALTER TABLE ... ALTER COLUMN ... SET STATISTICS (see ALTER TABLE
84       (ALTER_TABLE(7))). The target value sets the maximum number of entries
85       in the most-common-value list and the maximum number of bins in the
86       histogram. The default target value is 100, but this can be adjusted up
87       or down to trade off accuracy of planner estimates against the time
88       taken for ANALYZE and the amount of space occupied in pg_statistic. In
89       particular, setting the statistics target to zero disables collection
90       of statistics for that column. It might be useful to do that for
91       columns that are never used as part of the WHERE, GROUP BY, or ORDER BY
92       clauses of queries, since the planner will have no use for statistics
93       on such columns.
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95       The largest statistics target among the columns being analyzed
96       determines the number of table rows sampled to prepare the statistics.
97       Increasing the target causes a proportional increase in the time and
98       space needed to do ANALYZE.
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100       One of the values estimated by ANALYZE is the number of distinct values
101       that appear in each column. Because only a subset of the rows are
102       examined, this estimate can sometimes be quite inaccurate, even with
103       the largest possible statistics target. If this inaccuracy leads to bad
104       query plans, a more accurate value can be determined manually and then
105       installed with ALTER TABLE ... ALTER COLUMN ... SET (n_distinct = ...)
106       (see ALTER TABLE (ALTER_TABLE(7))).
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108       If the table being analyzed has one or more children, ANALYZE will
109       gather statistics twice: once on the rows of the parent table only, and
110       a second time on the rows of the parent table with all of its children.
111       This second set of statistics is needed when planning queries that
112       traverse the entire inheritance tree. The autovacuum daemon, however,
113       will only consider inserts or updates on the parent table itself when
114       deciding whether to trigger an automatic analyze for that table. If
115       that table is rarely inserted into or updated, the inheritance
116       statistics will not be up to date unless you run ANALYZE manually.
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118       If any of the child tables are foreign tables whose foreign data
119       wrappers do not support ANALYZE, those child tables are ignored while
120       gathering inheritance statistics.
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122       If the table being analyzed is completely empty, ANALYZE will not
123       record new statistics for that table. Any existing statistics will be
124       retained.
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COMPATIBILITY

127       There is no ANALYZE statement in the SQL standard.
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SEE ALSO

130       VACUUM(7), vacuumdb(1), Section 19.4.4, Section 24.1.6
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134PostgreSQL 10.7                      2019                           ANALYZE(7)
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