diff options
| -rw-r--r-- | doc/src/sgml/pgstatstatements.sgml | 18 |
1 files changed, 16 insertions, 2 deletions
diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml index a58ecf7065f..ca9478acdf6 100644 --- a/doc/src/sgml/pgstatstatements.sgml +++ b/doc/src/sgml/pgstatstatements.sgml @@ -242,7 +242,7 @@ </para> <para> - Consumers of <literal>pg_stat_statements</> may wish to use + Consumers of <structname>pg_stat_statements</> may wish to use <structfield>queryid</> (perhaps in combination with <structfield>dbid</> and <structfield>userid</>) as a more stable and reliable identifier for each entry than its query text. @@ -252,7 +252,7 @@ post-parse-analysis tree, its value is a function of, among other things, the internal object identifiers appearing in this representation. This has some counterintuitive implications. For example, - <literal>pg_stat_statements</> will consider two apparently-identical + <filename>pg_stat_statements</> will consider two apparently-identical queries to be distinct, if they reference a table that was dropped and recreated between the executions of the two queries. The hashing process is also sensitive to differences in @@ -272,6 +272,20 @@ not be a useful identifier for accumulating costs across a set of logical replicas. If in doubt, direct testing is recommended. </para> + + <para> + The representative query texts are kept in an external disk file, and do + not consume shared memory. Therefore, even very lengthy query texts can + be stored successfully. However, if many long query texts are + accumulated, the external file might grow unmanageably large. As a + recovery method if that happens, <filename>pg_stat_statements</> may + choose to discard the query texts, whereupon all existing entries in + the <structname>pg_stat_statements</> view will show + null <structfield>query</> fields, though the statistics associated with + each <structfield>queryid</> are preserved. If this happens, consider + reducing <varname>pg_stat_statements.max</varname> to prevent + recurrences. + </para> </sect2> <sect2> |