From 7e9ed623d9988fcb1497a2a8ca7f676a5bfa136f Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Thu, 19 Mar 2015 22:38:12 -0400
Subject: [PATCH] docs: mention the optimizer can increase the index usage
count
Report by Marko Tiikkaja
---
doc/src/sgml/monitoring.sgml | 7 +++++--
1 file 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>
--
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