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13th chunk of `doc/src/sgml/glossary.sgml`
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    <para>
     The instance handles all key features of a <acronym>DBMS</acronym>:
     read and write access to files and shared memory,
     assurance of the <acronym>ACID</acronym> properties,
     <glossterm linkend="glossary-connection">connections</glossterm> to
     <glossterm linkend="glossary-client">client processes</glossterm>,
     privilege verification, crash recovery, replication, etc.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-isolation">
   <glossterm>Isolation</glossterm>
   <glossdef>
    <para>
     The property that the effects of a transaction are not visible to
     <glossterm linkend="glossary-concurrency">concurrent transactions</glossterm>
     before it commits.
     This is one of the <acronym>ACID</acronym> properties.
    </para>
    <para>
     For more information, see <xref linkend="transaction-iso" />.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-join">
   <glossterm>Join</glossterm>
   <glossdef>
    <para>
     An operation and <acronym>SQL</acronym> keyword used in
     <glossterm linkend="glossary-query">queries</glossterm>
     for combining data from multiple
     <glossterm linkend="glossary-relation">relations</glossterm>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-key">
   <glossterm>Key</glossterm>
   <glossdef>
    <para>
     A means of identifying a <glossterm linkend="glossary-tuple">row</glossterm> within a
     <glossterm linkend="glossary-table">table</glossterm> or
     other <glossterm linkend="glossary-relation">relation</glossterm> by
     values contained within one or more
     <glossterm linkend="glossary-attribute">attributes</glossterm>
     in that relation.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-lock">
   <glossterm>Lock</glossterm>
   <glossdef>
    <para>
     A mechanism that allows a process to limit or prevent simultaneous
     access to a resource.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-log-file">
   <glossterm>Log file</glossterm>
   <glossdef>
    <para>
     Log files contain human-readable text lines about events.
     Examples include login failures, long-running queries, etc.
    </para>
    <para>
     For more information, see
     <xref linkend="logfile-maintenance"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-logged">
   <glossterm>Logged</glossterm>
   <glossdef>
    <para>
     A <glossterm linkend="glossary-table">table</glossterm> is considered
     <glossterm linkend="glossary-logged">logged</glossterm> if changes to it are sent to the
     <glossterm linkend="glossary-wal">WAL</glossterm>. By default, all regular
     tables are logged. A table can be specified as
     <glossterm linkend="glossary-unlogged">unlogged</glossterm> either at
     creation time or via the <command>ALTER TABLE</command> command.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-logger">
   <glossterm>Logger (process)</glossterm>
   <glossdef>
    <para>
     An <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>
     which, if enabled, writes information about database events into the current
     <glossterm linkend="glossary-log-file">log file</glossterm>.
     When reaching certain time- or
     volume-dependent criteria, a new log file is created.
     Also called <firstterm>syslogger</firstterm>.
    </para>
    <para>
     For more information, see
     <xref linkend="runtime-config-logging"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-logical-replication-cluster">
   <glossterm>Logical replication cluster</glossterm>
   <glossdef>
    <para>
     A set of publisher and subscriber instances with the publisher instance
     replicating changes to the subscriber instance.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-log-record">
   <glossterm>Log record</glossterm>
    <glossdef>
     <para>
Title: Database Concepts: Instance, Isolation, Join, and Other Key Terms
Summary
This section covers several important database concepts in PostgreSQL. It describes a database instance as handling key DBMS features including file access, ACID properties, client connections, and more. Isolation is defined as an ACID property where transaction effects are not visible to concurrent transactions before commit. The text introduces the concept of a Join as an SQL operation for combining data from multiple relations. It also defines a Key as a means of identifying rows in a table, and a Lock as a mechanism to limit resource access. The passage further explains Log files, Logged tables, the Logger process, and briefly mentions Logical replication clusters. These concepts are fundamental to understanding database operations and management in PostgreSQL.