<entry><structname>pg_statio_user_sequences</structname><indexterm><primary>pg_statio_user_sequences</primary></indexterm></entry>
      <entry>Same as <structname>pg_statio_all_sequences</structname>, except that only
      user sequences are shown.</entry>
     </row>

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

  <para>
   The per-index statistics are particularly useful to determine which
   indexes are being used and how effective they are.
  </para>

  <para>
   The <structname>pg_stat_io</structname> and
   <structname>pg_statio_</structname> set of views are useful for determining
   the effectiveness of the buffer cache. They can be used to calculate a cache
   hit ratio. Note that while <productname>PostgreSQL</productname>'s I/O
   statistics capture most instances in which the kernel was invoked in order
   to perform I/O, they do not differentiate between data which had to be
   fetched from disk and that which already resided in the kernel page cache.
   Users are advised to use the <productname>PostgreSQL</productname>
   statistics views in combination with operating system utilities for a more
   complete picture of their database's I/O performance.
  </para>

 </sect2>

 <sect2 id="monitoring-pg-stat-activity-view">
  <title><structname>pg_stat_activity</structname></title>

  <indexterm>
   <primary>pg_stat_activity</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_activity</structname> view will have one row
   per server process, showing information related to
   the current activity of that process.
  </para>

  <table id="pg-stat-activity-view" xreflabel="pg_stat_activity">
   <title><structname>pg_stat_activity</structname> View</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>datid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the database this backend is connected to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datname</structfield> <type>name</type>
      </para>
      <para>
       Name of the database this backend is connected to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of this backend
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>leader_pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of the parallel group leader if this process is a parallel
       query worker, or process ID of the leader apply worker if this process
       is a parallel apply worker.  <literal>NULL</literal> indicates that this
       process is a parallel group leader or leader apply worker, or does not
       participate in any parallel operation.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usesysid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the user logged into this backend
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usename</structfield> <type>name</type>
      </para>
      <para>
       Name of the user logged into this backend
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>application_name</structfield> <type>text</type>
      </para>
      <para>
       Name of the application that is connected