</row>

     <row>
      <entry role="catalog_table_entry">
       <para role="column_definition">
        <structfield>reads</structfield> <type>bigint</type>
       </para>
       <para>
        Number of read operations.
       </para>
      </entry>
     </row>

     <row>
      <entry role="catalog_table_entry">
       <para role="column_definition">
        <structfield>read_bytes</structfield> <type>numeric</type>
       </para>
       <para>
        The total size of read operations in bytes.
       </para>
      </entry>
     </row>

     <row>
      <entry role="catalog_table_entry">
       <para role="column_definition">
        <structfield>read_time</structfield> <type>double precision</type>
       </para>
       <para>
        Time spent waiting for read operations in milliseconds (if
        <xref linkend="guc-track-io-timing"/> is enabled and
        <varname>object</varname> is not <literal>wal</literal>,
        or if <xref linkend="guc-track-wal-io-timing"/> is enabled
        and <varname>object</varname> is <literal>wal</literal>,
        otherwise zero)
       </para>
      </entry>
     </row>

     <row>
      <entry role="catalog_table_entry">
       <para role="column_definition">
        <structfield>writes</structfield> <type>bigint</type>
       </para>
       <para>
        Number of write operations.
       </para>
      </entry>
     </row>

     <row>
      <entry role="catalog_table_entry">
       <para role="column_definition">
        <structfield>write_bytes</structfield> <type>numeric</type>
       </para>
       <para>
        The total size of write operations in bytes.
       </para>
      </entry>
     </row>

     <row>
      <entry role="catalog_table_entry">
       <para role="column_definition">
        <structfield>write_time</structfield> <type>double precision</type>
       </para>
       <para>
        Time spent waiting for write operations in milliseconds (if
        <xref linkend="guc-track-io-timing"/> is enabled and
        <varname>object</varname> is not <literal>wal</literal>,
        or if <xref linkend="guc-track-wal-io-timing"/> is enabled
        and <varname>object</varname> is <literal>wal</literal>,
        otherwise zero)
       </para>
      </entry>
     </row>

     <row>
      <entry role="catalog_table_entry">
       <para role="column_definition">
        <structfield>writebacks</structfield> <type>bigint</type>
       </para>
       <para>
        Number of units of size <symbol>BLCKSZ</symbol> (typically 8kB) which
        the process requested the kernel write out to permanent storage.
       </para>
      </entry>
     </row>

     <row>
      <entry role="catalog_table_entry">
       <para role="column_definition">
        <structfield>writeback_time</structfield> <type>double precision</type>
       </para>
       <para>
        Time spent waiting for writeback operations in milliseconds (if
        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero). This
        includes the time spent queueing write-out requests and, potentially,
        the time spent to write out the dirty data.
       </para>
      </entry>
     </row>

     <row>
      <entry role="catalog_table_entry">
       <para role="column_definition">
        <structfield>extends</structfield> <type>bigint</type>
       </para>
       <para>
        Number of relation extend operations.
       </para>
      </entry>
     </row>

     <row>
      <entry role="catalog_table_entry">
       <para role="column_definition">
        <structfield>extend_bytes</structfield> <type>numeric</type>
       </para>
       <para>
        The total size of relation extend operations in bytes.
       </para>
      </entry>
     </row>

     <row>
      <entry role="catalog_table_entry">
       <para role="column_definition">
        <structfield>extend_time</structfield> <type>double precision</type>
       </para>
       <para>
        Time spent waiting for extend operations in milliseconds.