process</glossterm>.
    </para>

    <para>
     For more information, see
     <xref linkend="warm-standby"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry>
   <glossterm>WAL segment</glossterm>
   <glosssee otherterm="glossary-wal-file" />
  </glossentry>

  <glossentry id="glossary-wal-sender">
   <glossterm>WAL sender (process)</glossterm>
   <glossdef>
    <para>
     A special <glossterm linkend="glossary-backend">backend process</glossterm>
     that streams WAL over a network.  The receiving end can be a
     <glossterm linkend="glossary-wal-receiver">WAL receiver</glossterm>
     in a <glossterm linkend="glossary-replica">replica</glossterm>,
     <xref linkend="app-pgreceivewal"/>, or any other client program
     that speaks the replication protocol.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-wal-summarizer">
   <glossterm>WAL summarizer (process)</glossterm>
   <glossdef>
    <para>
     An <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>
     that summarizes WAL data for
     <glossterm linkend="glossary-incremental-backup">incremental backups</glossterm>.
    </para>
    <para>
     For more information, see <xref linkend="runtime-config-wal-summarization"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-wal-writer">
   <glossterm>WAL writer (process)</glossterm>
   <glossdef>
    <para>
     An <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>
     that writes <glossterm linkend="glossary-wal-record">WAL records</glossterm>
     from <glossterm linkend="glossary-shared-memory">shared memory</glossterm> to
     <glossterm linkend="glossary-wal-file">WAL files</glossterm>.
    </para>
    <para>
     For more information, see
     <xref linkend="runtime-config-wal"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-window-function">
   <glossterm>Window function (routine)</glossterm>
   <glossdef>
    <para>
     A type of <glossterm linkend="glossary-function">function</glossterm>
     used in a <glossterm linkend="glossary-query">query</glossterm>
     that applies to a <glossterm linkend="glossary-partition">partition</glossterm>
     of the query's <glossterm linkend="glossary-result-set">result set</glossterm>;
     the function's result is based on values found in
     <glossterm linkend="glossary-tuple">rows</glossterm> of the same partition or frame.
    </para>
    <para>
     All <glossterm linkend="glossary-aggregate">aggregate functions</glossterm>
     can be used as window functions, but window functions can also be
     used to, for example, give ranks to each of the rows in the partition.
     Also known as <firstterm>analytic functions</firstterm>.
    </para>
    <para>
     For more information, see
     <xref linkend="tutorial-window"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-wal">
   <glossterm>Write-ahead log</glossterm>
   <glossdef>
    <para>
     The journal that keeps track of the changes in the
     <glossterm linkend="glossary-db-cluster">database cluster</glossterm>
     as user- and system-invoked operations take place.
     It comprises many individual
     <glossterm linkend="glossary-wal-record">WAL records</glossterm> written
     sequentially to <glossterm linkend="glossary-wal-file">WAL files</glossterm>.
    </para>
   </glossdef>
  </glossentry>
 </glosslist>
</appendix>