postgres.git / summary / log / commit / refs

commit    6da67a0c111a29e876b7172d081c7d152d23ea3d
Author:   Michael Paquier <michael@paquier.xyz>
Date:     Wed Mar 01 01:47:01 2023 +0000
First released in: 16.0

    doc: Mention de-normalization of deallocated entries in pg_stat_statements
    
    The current implementation of query normalization in pg_stat_statements
    is optimistic.  If an entry is deallocated between the post-analyze hook
    and the planner and/or execution hook, it can be possible to find query
    strings with literal constant values (like "SELECT 1, 2") rather than
    their normalized flavor (like "SELECT $1, $2").
    
    This commit adds in the documentation a paragraph about this limitation,
    and that this risk can be reduced by increasing pg_stat_statements.max,
    particularly if pg_stat_statements_info reports a high number of
    deallocations.
    
    Author: Sami Imseih
    Discussion: https://postgr.es/m/9CFF3512-355B-4676-8CCC-6CF622F4DC1A@amazon.com


 doc/src/sgml/pgstatstatements.sgml | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml
index 0b40e1eea3a..b1214ee6453 100644
--- a/doc/src/sgml/pgstatstatements.sgml
+++ b/doc/src/sgml/pgstatstatements.sgml
@@ -516,6 +516,16 @@
    <structname>pg_stat_statements</structname> entry.
   </para>
 
+  <para>
+   Queries on which normalization can be applied may be observed with constant
+   values in <structname>pg_stat_statements</structname>, especially when there
+   is a high rate of entry deallocations. To reduce the likelihood of this
+   happening, consider increasing <varname>pg_stat_statements.max</varname>.
+   The <structname>pg_stat_statements_info</structname> view, discussed below
+   in <xref linkend="pgstatstatements-pg-stat-statements-info"/>,
+   provides statistics about entry deallocations.
+  </para>
+
   <para>
    In some cases, queries with visibly different texts might get merged into a
    single <structname>pg_stat_statements</structname> entry.  Normally this will happen


[parent: 6a88a058614b]