File: cnid_dbd.8.xml

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<?xml version="1.0" encoding="UTF-8"?>
<refentry id="cnid_dbd.8">
  <refmeta>
    <refentrytitle>cnid_dbd</refentrytitle>

    <manvolnum>8</manvolnum>

    <refmiscinfo class="date">10 Nov 2015</refmiscinfo>

    <refmiscinfo class="source">@NETATALK_VERSION@</refmiscinfo>
  </refmeta>

  <refnamediv>
    <refname>cnid_dbd</refname>

    <refpurpose>implement access to CNID databases through a dedicated daemon
    process</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <cmdsynopsis>
      <command>cnid_dbd</command>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>cnid_dbd</command>

        <group choice="plain">
          <arg choice="plain">-v</arg>
          <arg choice="plain">-V</arg>
        </group>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>DESCRIPTION</title>

    <para><command>cnid_dbd</command> provides an interface for storage and
    retrieval of catalog node IDs (CNIDs) and related information to the
    <emphasis remap="B">afpd</emphasis> daemon. CNIDs are a component of
    Macintosh based file systems with semantics that map not easily onto Unix
    file systems. This makes separate storage in a database necessary.
    <command>cnid_dbd</command> is part of the <emphasis remap="B">CNID
    backend</emphasis> framework of <emphasis remap="B">afpd</emphasis> and
    implements the <emphasis remap="B">dbd</emphasis> backend.</para>

    <para><command>cnid_dbd</command> is never started via the command line or
    system startup scripts but only by the <emphasis
    remap="B">cnid_metad</emphasis> daemon. There is one instance of
    <command>cnid_dbd</command> per netatalk volume.</para>

    <para><command>cnid_dbd</command> uses the <emphasis remap="B">Berkeley
    DB</emphasis> database library and uses transactionally protected updates.
    The <emphasis remap="B">dbd</emphasis> backend with transactions will
    avoid corruption of the CNID database even if the system crashes
    unexpectedly.</para>

    <para><command>cnid_dbd</command> inherits the effective userid and
    groupid from <emphasis remap="B">cnid_metad</emphasis> on startup, which
    is normally caused by <emphasis remap="B">afpd</emphasis> serving a
    netatalk volume to a client. It changes to the <emphasis
    remap="B">Berkeley DB</emphasis> database home directory <emphasis
    remap="I">dbdir</emphasis> that is associated with the volume. If the
    userid inherited from <emphasis remap="B">cnid_metad</emphasis> is 0
    (root), <command>cnid_dbd</command> will change userid and groupid to the
    owner and group of the database home directory. Otherwise, it will
    continue to use the inherited values. <command>cnid_dbd</command> will
    then attempt to open the database and start serving requests using
    filedescriptor <emphasis remap="I">clntfd</emphasis>. Subsequent instances
    of <emphasis remap="B">afpd</emphasis> that want to access the same volume
    are redirected to the running <command>cnid_dbd</command> process by
    <emphasis remap="B">cnid_metad</emphasis> via the filedescriptor <emphasis
    remap="I">ctrlfd</emphasis>.</para>

    <para><command>cnid_dbd</command> can be configured to run forever or to
    exit after a period of inactivity. If <command>cnid_dbd</command> receives
    a TERM or an INT signal it will exit cleanly after flushing dirty database
    buffers to disk and closing <emphasis remap="B">Berkeley DB</emphasis>
    database environments. It is safe to terminate <command>cnid_dbd</command>
    this way, it will be restarted when necessary. Other signals are not
    handled and will cause an immediate exit, possibly leaving the CNID
    database in an inconsistent state (no transactions) or losing recent
    updates during recovery (transactions).</para>

    <para>The <emphasis remap="B">Berkeley DB</emphasis> database subsystem
    will create files named log.xxxxxxxxxx in the database home directory
    <emphasis remap="I">dbdir</emphasis>, where xxxxxxxxxx is a monotonically
    increasing integer. These files contain the transactional database
    changes. They will be removed regularly, unless the <emphasis
    remap="B">logfile_autoremove</emphasis> option is specified in the
    <emphasis remap="I">db_param</emphasis> configuration file (see
    below) with a value of 0 (default 1).</para>
  </refsect1>

  <refsect1>
    <title>OPTIONS</title>

    <variablelist remap="TP">
      <varlistentry>
        <term><option>-v, -V</option></term>
	
        <listitem>
          <para>Show version and exit.</para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>CONFIGURATION</title>

    <para><command>cnid_dbd</command> reads configuration information from the
    file <emphasis remap="I">db_param</emphasis> in the database directory
    <emphasis remap="I">dbdir</emphasis> on startup. If the file does not
    exist or a parameter is not listed, suitable default values are used. The
    format for a single parameter is the parameter name, followed by one or
    more spaces, followed by the parameter value, followed by a newline. The
    following parameters are currently recognized:</para>

    <variablelist remap="TP">
      <varlistentry>
        <term><emphasis remap="B">logfile_autoremove</emphasis></term>

        <listitem>
          <para>If set to 0, unused Berkeley DB transactional logfiles
          (log.xxxxxxxxxx in the database home directory) are not removed on
          startup of <command>cnid_dbd</command> and on a regular basis.
          Default: 1.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis remap="B">cachesize</emphasis></term>

        <listitem>
          <para>Determines the size of the Berkeley DB cache in kilobytes.
          Default: 8192. Each <command>cnid_dbd</command> process grabs that
          much memory on top of its normal memory footprint. It can be used to
          tune database performance. The <emphasis
          remap="B">db_stat</emphasis> utility with the <option>-m</option>
          option that comes with Berkley DB can help you determine whether you
          need to change this value. The default is pretty conservative so
          that a large percentage of requests should be satisfied from the
          cache directly. If memory is not a bottleneck on your system you
          might want to leave it at that value. The <emphasis
          remap="B">Berkeley DB Tutorial and Reference Guide</emphasis> has a
          section <emphasis remap="B">Selecting a cache size</emphasis> that
          gives more detailed information.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis remap="B">flush_frequency</emphasis></term>

        <term><emphasis remap="B">flush_interval</emphasis></term>

        <listitem>
          <para><emphasis remap="I">flush_frequency</emphasis> (Default: 1000)
          and <emphasis remap="I">flush_interval</emphasis> (Default: 1800)
          control how often changes to the database are checkpointed. Both of
          these operations are performed if either i) more than <emphasis
          remap="I">flush_frequency</emphasis> requests have been received or
          ii) more than <emphasis remap="I">flush_interval</emphasis> seconds
          have elapsed since the last save/checkpoint. Be careful to check
          your harddisk configuration for on disk cache settings. Many IDE
          disks just cache writes as the default behaviour, so even flushing
          database files to disk will not have the desired effect.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis remap="B">fd_table_size</emphasis></term>

        <listitem>
          <para>is the maximum number of connections (filedescriptors) that
          can be open for <emphasis remap="B">afpd</emphasis> client processes
          in <emphasis remap="B">cnid_dbd.</emphasis> Default: 512. If this
          number is exceeded, one of the existing connections is closed and
          reused. The affected <emphasis remap="B">afpd</emphasis> process
          will transparently reconnect later, which causes slight overhead. On
          the other hand, setting this parameter too high could affect
          performance in <command>cnid_dbd</command> since all descriptors
          have to be checked in a <function>select()</function> system call,
          or worse, you might exceed the per process limit of open file
          descriptors on your system. It is safe to set the value to 1 on
          volumes where only one <emphasis remap="B">afpd</emphasis> client
          process is expected to run, e.g. home directories.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis remap="B">idle_timeout</emphasis></term>

        <listitem>
          <para>is the number of seconds of inactivity before an idle
          <command>cnid_dbd</command> exits. Default: 600. Set this to 0 to
          disable the timeout.</para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>UPDATING</title>

    <para>Note that the first version to appear <emphasis>after</emphasis>
    Netatalk 2.1 i.e. Netatalk 2.1.1, will support BerkeleyDB updates on the fly
    without manual intervention. In other words Netatalk 2.1 does contain code
    to prepare the BerkeleyDB database for upgrades and to upgrade it in case
    it has been prepared before. That means it can't upgrade a 2.0.x version
    because that one didn't prepare the database.</para>

    <para>In order to update between older Netatalk releases using different
    BerkeleyDB library versions, follow this steps:</para>

    <itemizedlist>
      <listitem>
        <para>Stop the to be upgraded old version of Netatalk</para>
      </listitem>

      <listitem>
        <para>Using the old BerkeleyDB utilities run <command>db_recover -h
        &lt;path to .AppleDB&gt;</command></para>
      </listitem>

      <listitem>
        <para>Using the new BerkeleyDB utilities run <command>db_upgrade -v -h
        &lt;path to .AppleDB&gt; -f cnid2.db</command></para>
      </listitem>

      <listitem>
        <para>Again using the new BerkeleyDB utilities run
        <command>db_checkpoint -1 -h &lt;path to .AppleDB&gt;</command></para>
      </listitem>

      <listitem>
        <para>Start the the new version of Netatalk</para>
      </listitem>
    </itemizedlist>

  </refsect1>

  <refsect1>
    <title>SEE ALSO</title>

    <para><citerefentry>
        <refentrytitle>cnid_metad</refentrytitle>

        <manvolnum>8</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>afpd</refentrytitle>

        <manvolnum>8</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>dbd</refentrytitle>

        <manvolnum>1</manvolnum>
      </citerefentry></para>
  </refsect1>
</refentry>