buffers in the relation to be evicted from the buffer pool
  given a relation identifier.  Use of this function is restricted to
  superusers only.
 </para>

 <para>
  The <function>pg_buffercache_evict_all()</function> function allows all
  unpinned shared buffers to be evicted in the buffer pool.  Use of this
  function is restricted to superusers only.
 </para>

 <sect2 id="pgbuffercache-pg-buffercache">
  <title>The <structname>pg_buffercache</structname> View</title>

  <para>
   The definitions of the columns exposed by the view are shown in <xref linkend="pgbuffercache-columns"/>.
  </para>

  <table id="pgbuffercache-columns">
   <title><structname>pg_buffercache</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>bufferid</structfield> <type>integer</type>
      </para>
      <para>
       ID, in the range 1..<varname>shared_buffers</varname>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relfilenode</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relfilenode</structfield>)
      </para>
      <para>
       Filenode number of the relation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>reltablespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Tablespace OID of the relation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>reldatabase</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-database"><structname>pg_database</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Database OID of the relation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relforknumber</structfield> <type>smallint</type>
      </para>
      <para>
       Fork number within the relation;  see
       <filename>common/relpath.h</filename>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relblocknumber</structfield> <type>bigint</type>
      </para>
      <para>
       Page number within the relation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>isdirty</structfield> <type>boolean</type>
      </para>
      <para>
       Is the page dirty?
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usagecount</structfield> <type>smallint</type>
      </para>
      <para>
       Clock-sweep access count
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pinning_backends</structfield> <type>integer</type>
      </para>
      <para>
       Number of backends pinning this buffer
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   There is one row for each buffer in the shared cache. Unused buffers are
   shown with all fields null except <structfield>bufferid</structfield>.  Shared system
   catalogs are shown as belonging to database zero.
  </para>

  <para>
   Because the cache is shared by all the databases, there