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>pid</structfield> <type>int4</type>
      </para>
      <para>
       Process ID of the server process that is issuing this I/O.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>io_id</structfield> <type>int4</type>
      </para>
      <para>
       Identifier of the I/O handle. Handles are reused once the I/O
       completed (or if the handle is released before I/O is started). On reuse
       <link linkend="view-pg-aios-io-generation">
        <structname>pg_aios</structname>.<structfield>io_generation</structfield>
       </link>
       is incremented.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry" id="view-pg-aios-io-generation"><para role="column_definition">
       <structfield>io_generation</structfield> <type>int8</type>
      </para>
      <para>
       Generation of the I/O handle.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>state</structfield> <type>text</type>
      </para>
      <para>
       State of the I/O handle:
       <itemizedlist>
        <listitem>
         <para>
          <literal>HANDED_OUT</literal>, referenced by code but not yet used
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>DEFINED</literal>, information necessary for execution is known
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>STAGED</literal>, ready for execution
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>SUBMITTED</literal>, submitted for execution
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>COMPLETED_IO</literal>, finished, but result has not yet been processed
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>COMPLETED_SHARED</literal>, shared completion processing completed
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>COMPLETED_LOCAL</literal>, backend local completion processing completed
         </para>
        </listitem>
       </itemizedlist>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>operation</structfield> <type>text</type>
      </para>
      <para>
       Operation performed using the I/O handle:
       <itemizedlist>
        <listitem>
         <para>
          <literal>invalid</literal>, not yet known
         </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