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 is called a
     <glossterm linkend="glossary-database">database</glossterm> in
     <productname>PostgreSQL</productname>'s terminology.
    </para>
    <para>
     (Don't confuse this term with
     <glossterm linkend="glossary-system-catalog">system catalog</glossterm>).
    </para>
    <para>
     For more information, see
     <xref linkend="manage-ag-overview"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-check-constraint">
   <glossterm>Check constraint</glossterm>
   <glossdef>
    <para>
     A type of <glossterm linkend="glossary-constraint">constraint</glossterm>
     defined on a <glossterm linkend="glossary-relation">relation</glossterm>
     which restricts the values allowed in one or more
     <glossterm linkend="glossary-attribute">attributes</glossterm>. The
     check constraint can make reference to any attribute of the same row in
     the relation, but cannot reference other rows of the same relation or
     other relations.
    </para>
    <para>
     For more information, see
     <xref linkend="ddl-constraints"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-checkpoint">
   <glossterm>Checkpoint</glossterm>
   <glossdef>
    <para>
     A point in the <glossterm linkend="glossary-wal">WAL</glossterm> sequence
     at which it is guaranteed that the heap and index data files have been
     updated with all information from
     <glossterm linkend="glossary-shared-memory">shared memory</glossterm>
     modified before that checkpoint;
     a <firstterm>checkpoint record</firstterm> is written and flushed to WAL
     to mark that point.
    </para>
    <para>
     A checkpoint is also the act of carrying out all the actions that
     are necessary to reach a checkpoint as defined above.
     This process is initiated when predefined conditions are met,
     such as a specified amount of time has passed, or a certain volume
     of records has been written; or it can be invoked by the user
     with the command <command>CHECKPOINT</command>.
    </para>
    <para>
     For more information, see
     <xref linkend="wal-configuration"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-checkpointer">
   <glossterm>Checkpointer (process)</glossterm>
   <glossdef>
    <para>
     An <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>
     that is responsible for executing
     <glossterm linkend="glossary-checkpoint">checkpoints</glossterm>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry>
   <glossterm>Class (archaic)</glossterm>
   <glosssee otherterm="glossary-relation" />
  </glossentry>

  <glossentry id="glossary-client">
   <glossterm>Client (process)</glossterm>
   <glossdef>
    <para>
     Any process, possibly remote, that establishes a
     <glossterm linkend="glossary-session">session</glossterm>
     by <glossterm linkend="glossary-connection">connecting</glossterm> to an
     <glossterm linkend="glossary-instance">instance</glossterm>