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| author | Bruce Momjian <bruce@momjian.us> | 2020-11-12 15:00:44 -0500 |
|---|---|---|
| committer | Bruce Momjian <bruce@momjian.us> | 2020-11-12 15:00:44 -0500 |
| commit | b740b4a86784f40a4a473dc754525919e6abbc22 (patch) | |
| tree | 49f141819feff7845833324a3c9bca217bf90e0b | |
| parent | b5b7072a6725a2564c43b88feb5c7bb38862d4e8 (diff) | |
| download | postgresql-b740b4a86784f40a4a473dc754525919e6abbc22.tar.gz postgresql-b740b4a86784f40a4a473dc754525919e6abbc22.zip | |
docs: mention that expression indexes need analyze
Expression indexes can't benefit from pre-computed statistics on
columns.
Reported-by: Nikolay Samokhvalov
Discussion: https://postgr.es/m/CANNMO++5rw9RDA=p40iMVbMNPaW6O=S0AFzTU=KpYHRpCd1voA@mail.gmail.com
Author: Nikolay Samokhvalov, modified
Backpatch-through: 9.5
| -rw-r--r-- | doc/src/sgml/ref/create_index.sgml | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/doc/src/sgml/ref/create_index.sgml b/doc/src/sgml/ref/create_index.sgml index 8c62b21089c..06a1ddf33fe 100644 --- a/doc/src/sgml/ref/create_index.sgml +++ b/doc/src/sgml/ref/create_index.sgml @@ -676,6 +676,16 @@ Indexes: </para> <para> + The regularly system collects statistics on all of a table's + columns. Newly-created non-expression indexes can immediately + use these statistics to determine an index's usefulness. + For new expression indexes, it is necessary to run <link + linkend="sql-analyze"><command>ANALYZE</command></link> or wait for + the <link linkend="autovacuum">autovacuum daemon</link> to analyze + the table to generate statistics about new expression indexes. + </para> + + <para> For most index methods, the speed of creating an index is dependent on the setting of <xref linkend="guc-maintenance-work-mem"/>. Larger values will reduce the time needed for index creation, so long |