linkend="glossary-mvcc">multiversion concurrency control</glossterm>
     mechanism.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-connection">
   <glossterm>Connection</glossterm>
   <glossdef>
    <para>
     An established line of communication between a client process and a
     <glossterm linkend="glossary-backend">backend</glossterm> process,
     usually over a network, supporting a
     <glossterm linkend="glossary-session">session</glossterm>.  This term is
     sometimes used as a synonym for session.
    </para>
    <para>
     For more information, see
     <xref linkend="runtime-config-connection"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-consistency">
   <glossterm>Consistency</glossterm>
   <glossdef>
    <para>
     The property that the data in the
     <glossterm linkend="glossary-database">database</glossterm>
     is always in compliance with
     <glossterm linkend="glossary-constraint">integrity constraints</glossterm>.
     Transactions may be allowed to violate some of the constraints
     transiently before it commits, but if such violations are not resolved
     by the time it commits, such a transaction is automatically
     <glossterm linkend="glossary-rollback">rolled back</glossterm>.
     This is one of the <acronym>ACID</acronym> properties.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-constraint">
   <glossterm>Constraint</glossterm>
   <glossdef>
    <para>
     A restriction on the values of data allowed within a
     <glossterm linkend="glossary-table">table</glossterm>,
     or in attributes of a
     <glossterm linkend="glossary-domain">domain</glossterm>.
    </para>
    <para>
     For more information, see
     <xref linkend="ddl-constraints"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-cumulative-statistics">
   <glossterm>Cumulative Statistics System</glossterm>
   <glossdef>
    <para>
     A system which, if enabled, accumulates statistical information
     about the <glossterm linkend="glossary-instance">instance</glossterm>'s
     activities.
    </para>
    <para>
      For more information, see
      <xref linkend="monitoring-stats"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry>
   <glossterm>Data area</glossterm>
   <glosssee otherterm="glossary-data-directory" />
  </glossentry>

  <glossentry id="glossary-database">
   <glossterm>Database</glossterm>
   <glossdef>
    <para>
     A named collection of
     <glossterm linkend="glossary-sql-object">local SQL objects</glossterm>.
    </para>
    <para>
     For more information, see
     <xref linkend="manage-ag-overview"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-db-cluster">
   <glossterm>Database cluster</glossterm>
   <glossdef>
    <para>
     A collection of databases and global SQL objects,
     and their common static and dynamic metadata.
     Sometimes referred to as a
     <firstterm>cluster</firstterm>.
     A database cluster is created using the
     <xref linkend="app-initdb" /> program.
    </para>
    <para>
     In <productname>PostgreSQL</productname>, the term
     <firstterm>cluster</firstterm> is also sometimes used to refer to an instance.
     (Don't confuse this term with the SQL command <command>CLUSTER</command>.)
    </para>
    <para>
     See also <glossterm linkend="glossary-cluster-owner">cluster owner</glossterm>,
     the operating-system owner of a cluster,
     and <glossterm linkend="glossary-bootstrap-superuser">bootstrap superuser</glossterm>,
     the <productname>PostgreSQL</productname> owner of a cluster.
    </para>
   </glossdef>
  </glossentry>

  <glossentry>
   <glossterm>Database server</glossterm>
   <glosssee otherterm="glossary-instance" />
  </glossentry>

  <glossentry id="glossary-database-superuser">
   <glossterm>Database superuser</glossterm>
   <glossdef>
    <para>
     A role having <firstterm>superuser status</firstterm>