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</filename> may
   choose to discard the query texts, whereupon all existing entries in
   the <structname>pg_stat_statements</structname> view will show
   null <structfield>query</structfield> fields, though the statistics associated with
   each <structfield>queryid</structfield> are preserved.  If this happens, consider
   reducing <varname>pg_stat_statements.max</varname> to prevent
   recurrences.
  </para>

  <para>
   <structfield>plans</structfield> and <structfield>calls</structfield> aren't
   always expected to match because planning and execution statistics are
   updated at their respective end phase, and only for successful operations.
   For example, if a statement is successfully planned but fails during
   the execution phase, only its planning statistics will be updated.
   If planning is skipped because a cached plan is used, only its execution
   statistics will be updated.
  </para>
 </sect2>

 <sect2 id="pgstatstatements-pg-stat-statements-info">
  <title>The <structname>pg_stat_statements_info</structname> View</title>

  <indexterm>
   <primary>pg_stat_statements_info</primary>
  </indexterm>

  <para>
   The statistics of the <filename>pg_stat_statements</filename> module
   itself are tracked and made available via a view named
   <structname>pg_stat_statements_info</structname>.  This view contains
   only a single row.  The columns of the view are shown in
   <xref linkend="pgstatstatementsinfo-columns"/>.
  </para>

  <table id="pgstatstatementsinfo-columns">
   <title><structname>pg_stat_statements_info</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>dealloc</structfield> <type>bigint</type>
      </para>
      <para>
       Total number of times <structname>pg_stat_statements</structname>
       entries about the least-executed statements were deallocated
       because more distinct statements than
       <varname>pg_stat_statements.max</varname> were observed
      </para></entry>
     </row>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time at which all statistics in the
       <structname>pg_stat_statements</structname> view were last reset.
      </para></entry>
     </row>

    </tbody>
   </tgroup>
  </table>
 </sect2>

 <sect2 id="pgstatstatements-funcs">
  <title>Functions</title>

  <variablelist>
   <varlistentry>
    <term>
     <function>pg_stat_statements_reset(userid Oid, dbid Oid, queryid
     bigint, minmax_only boolean) returns timestamp with time zone</function>
     <indexterm>
      <primary>pg_stat_statements_reset</primary>
     </indexterm>
    </term>

    <listitem>
     <para>
      <function>pg_stat_statements_reset</function> discards statistics
      gathered so far by <filename>pg_stat_statements</filename> corresponding
      to the specified <structfield>userid</structfield>, <structfield>dbid</structfield>
      and <structfield>queryid</structfield>.  If any of the parameters are not
      specified, the default value <literal>0</literal>(invalid) is used for
      each of them and the statistics that match with other parameters will be
      reset.  If no parameter is specified or all the specified parameters are
      <literal>0</literal>(invalid), it will discard all statistics.
      If all statistics in the <filename>pg_stat_statements</filename>