ordinarily
   necessary, since WAL summary files primarily exist to support
   <link linkend="backup-incremental-backup">incremental backup</link>,
   but it may be useful for debugging purposes.
  </para>

  <para>
   A WAL summary file is indexed by tablespace OID, relation OID, and relation
   fork. For each relation fork, it stores the list of blocks that were
   modified by WAL within the range summarized in the file. It can also
   store a "limit block," which is 0 if the relation fork was created or
   truncated within the relevant WAL range, and otherwise the shortest length
   to which the relation fork was truncated. If the relation fork was not
   created, deleted, or truncated within the relevant WAL range, the limit
   block is undefined or infinite and will not be printed by this tool.
  </para>
 </refsect1>

 <refsect1>
  <title>Options</title>

   <para>
    <variablelist>
     <varlistentry>
      <term><option>-i</option></term>
      <term><option>--individual</option></term>
      <listitem>
       <para>
        By default, <literal>pg_walsummary</literal> prints one line of output
        for each range of one or more consecutive modified blocks. This can
        make the output a lot briefer, since a relation where all blocks from
        0 through 999 were modified will produce only one line of output rather
        than 1000 separate lines. This option requests a separate line of
        output for every modified block.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-q</option></term>
      <term><option>--quiet</option></term>
      <listitem>
       <para>
        Do not print any output, except for errors. This can be useful
        when you want to know whether a WAL summary file can be successfully
        parsed but don't care about the contents.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-V</option></term>
      <term><option>--version</option></term>
      <listitem>
       <para>
        Display version information, then exit.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
       <term><option>-?</option></term>
       <term><option>--help</option></term>
       <listitem>
       <para>
       Shows help about <application>pg_walsummary</application> command line
       arguments, and exits.
       </para>
       </listitem>
     </varlistentry>

    </variablelist>
   </para>

 </refsect1>

 <refsect1>
  <title>Environment</title>

  <para>
   The environment variable <envar>PG_COLOR</envar> specifies whether to use
   color in diagnostic messages. Possible values are
   <literal>always</literal>, <literal>auto</literal> and
   <literal>never</literal>.
  </para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="app-pgbasebackup"/></member>
   <member><xref linkend="app-pgcombinebackup"/></member>
  </simplelist>
 </refsect1>

</refentry>