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| author | Bruce Momjian <bruce@momjian.us> | 2015-03-19 22:38:12 -0400 |
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| committer | Bruce Momjian <bruce@momjian.us> | 2015-03-19 22:38:15 -0400 |
| commit | 7e9ed623d9988fcb1497a2a8ca7f676a5bfa136f (patch) | |
| tree | 72acd73b22d1c8f1300e4b57cb65668ae8d303cc | |
| parent | 28beb69f8bc4ad7f0d1daca1095e1b47ffeaf011 (diff) | |
| download | postgresql-7e9ed623d9988fcb1497a2a8ca7f676a5bfa136f.tar.gz postgresql-7e9ed623d9988fcb1497a2a8ca7f676a5bfa136f.zip | |
docs: mention the optimizer can increase the index usage count
Report by Marko Tiikkaja
| -rw-r--r-- | doc/src/sgml/monitoring.sgml | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml index afcfb89a287..71d06ce513b 100644 --- a/doc/src/sgml/monitoring.sgml +++ b/doc/src/sgml/monitoring.sgml @@ -1382,8 +1382,8 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser </para> <para> - Indexes can be used via either simple index scans or <quote>bitmap</> - index scans. In a bitmap scan + Indexes can be used by simple index scans, <quote>bitmap</> index scans, + and the optimizer. In a bitmap scan the output of several indexes can be combined via AND or OR rules, so it is difficult to associate individual heap row fetches with specific indexes when a bitmap scan is used. Therefore, a bitmap @@ -1393,6 +1393,9 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser <structname>pg_stat_all_tables</>.<structfield>idx_tup_fetch</> count for the table, but it does not affect <structname>pg_stat_all_indexes</>.<structfield>idx_tup_fetch</>. + The optimizer also accesses indexes to check for supplied constants + whose values are outside the recorded range of the optimizer statistics + because the optimizer statistics might be stale. </para> <note> |