linkend="glossary-auxiliary-proc">auxiliary process</glossterm>
     that writes dirty
     <glossterm linkend="glossary-data-page">data pages</glossterm> from
     <glossterm linkend="glossary-shared-memory">shared memory</glossterm> to
     the file system.  It wakes up periodically, but works only for a short
     period in order to distribute its expensive <acronym>I/O</acronym>
     activity over time to avoid generating larger
     <acronym>I/O</acronym> peaks which could block other processes.
    </para>
    <para>
     For more information, see
     <xref linkend="runtime-config-resource-background-writer"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-basebackup">
   <glossterm>Base Backup</glossterm>
   <glossdef>
    <para>
     A binary copy of all
     <glossterm linkend="glossary-db-cluster">database cluster</glossterm>
     files. It is generated by the tool <xref linkend="app-pgbasebackup"/>.
     In combination with WAL files it can be used as the starting point
     for recovery, log shipping, or streaming replication.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-bloat">
   <glossterm>Bloat</glossterm>
   <glossdef>
    <para>
     Space in data pages which does not contain current row versions,
     such as unused (free) space or outdated row versions.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-bootstrap-superuser">
   <glossterm>Bootstrap superuser</glossterm>
   <glossdef>
    <para>
     The first <glossterm linkend="glossary-user">user</glossterm> initialized in a
     <glossterm linkend="glossary-db-cluster">database cluster</glossterm>.
    </para>
    <para>
     This user owns all system catalog tables in each database.  It is also the role
     from which all granted permissions originate.  Because of these things, this
     role may not be dropped.
    </para>
    <para>
     This role also behaves as a normal
     <glossterm linkend="glossary-database-superuser">database superuser</glossterm>,
     and its superuser status cannot be removed.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-buffer-access-strategy">
   <glossterm>Buffer Access Strategy</glossterm>
   <glossdef>
    <para>
     Some operations will access a large number of
     <glossterm linkend="glossary-data-page">pages</glossterm>.  A
     <firstterm>Buffer Access Strategy</firstterm> helps to prevent these
     operations from evicting too many pages from
     <glossterm linkend="glossary-shared-memory">shared buffers</glossterm>.
    </para>
    <para>
     A Buffer Access Strategy sets up references to a limited number of
     <glossterm linkend="glossary-shared-memory">shared buffers</glossterm> and
     reuses them circularly.  When the operation requires a new page, a victim
     buffer is chosen from the buffers in the strategy ring, which may require
     flushing the page's dirty data and possibly also unflushed
     <glossterm linkend="glossary-wal">WAL</glossterm> to permanent storage.
    </para>
    <para>
     Buffer Access Strategies are used for various operations such as
     sequential scans of large tables, <command>VACUUM</command>,
     <command>COPY</command>, <command>CREATE TABLE AS SELECT</command>,
     <command>ALTER TABLE</command>, <command>CREATE DATABASE</command>,
     <command>CREATE INDEX</command>, and <command>CLUSTER</command>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-cast">
   <glossterm>Cast</glossterm>
   <glossdef>
    <para>
     A conversion of a <glossterm linkend="glossary-datum">datum</glossterm>
     from its current data type to another data type.
    </para>
    <para>
     For more information, see
     <xref linkend="sql-createcast"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-catalog">
   <glossterm>Catalog</glossterm>
   <glossdef>
    <para>
     The <acronym>SQL</acronym> standard uses this term to
     indicate what