be released after a
     <glossterm linkend="glossary-checkpoint">checkpoint</glossterm>
     writes all the changes in it to the corresponding data files.
     Releasing the file can be done either by deleting it, or by changing its
     name so that it will be used in the future, which is called
     <firstterm>recycling</firstterm>.
    </para>
    <para>
     For more information, see
     <xref linkend="wal-internals"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-wal-record">
   <glossterm>WAL record</glossterm>
   <glossdef>
    <para>
     A low-level description of an individual data change.
     It contains sufficient information for the data change to be
     re-executed (<firstterm>replayed</firstterm>) in case a system failure
     causes the change to be lost.
     WAL records use a non-printable binary format.
    </para>
    <para>
     For more information, see
     <xref linkend="wal-internals"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-wal-receiver">
   <glossterm>WAL receiver (process)</glossterm>
   <glossdef>
    <para>
     An <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>
     that runs on a <glossterm linkend="glossary-replica">replica</glossterm>
     to receive WAL from the
     <glossterm linkend="glossary-primary-server">primary server</glossterm>
     for replay by the
     <glossterm linkend="glossary-startup-process">startup 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