</para>
        </listitem>
        <listitem>
         <para>
          <literal>readv</literal>, a vectored read
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>writev</literal>, a vectored write
         </para>
        </listitem>
       </itemizedlist>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>off</structfield> <type>int8</type>
      </para>
      <para>
       Offset of the I/O operation.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>length</structfield> <type>int8</type>
      </para>
      <para>
       Length of the I/O operation.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>target</structfield> <type>text</type>
      </para>
      <para>
       What kind of object is the I/O targeting:
       <itemizedlist spacing="compact">
        <listitem>
         <para>
          <literal>smgr</literal>, I/O on relations
         </para>
        </listitem>
       </itemizedlist>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>handle_data_len</structfield> <type>int2</type>
      </para>
      <para>
       Length of the data associated with the I/O operation. For I/O to/from
       <xref linkend="guc-shared-buffers"/> and <xref
       linkend="guc-temp-buffers"/>, this indicates the number of buffers the
       I/O is operating on.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>raw_result</structfield> <type>int4</type>
      </para>
      <para>
       Low-level result of the I/O operation, or NULL if the operation has not
       yet completed.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>result</structfield> <type>text</type>
      </para>
      <para>
       High-level result of the I/O operation:
       <itemizedlist>
        <listitem>
         <para>
          <literal>UNKNOWN</literal> means that the result of the
          operation is not yet known.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>OK</literal> means the I/O completed successfully.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>PARTIAL</literal> means that the I/O completed without
          error, but did not process all data. Commonly callers will need to
          retry and perform the remainder of the work in a separate I/O.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>WARNING</literal> means that the I/O completed without
          error, but that execution of the IO triggered a warning. E.g. when
          encountering a corrupted buffer with <xref
          linkend="guc-zero-damaged-pages"/> enabled.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>ERROR</literal> means the I/O failed with an error.
         </para>
        </listitem>
       </itemizedlist>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>target_desc</structfield> <type>text</type>
      </para>
      <para>
       Description of what the I/O operation is targeting.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>f_sync</structfield> <type>bool</type>
      </para>
      <para>
       Flag indicating whether the I/O is executed synchronously.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">