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<div class="section" id="server-side-caching">
<span id="server-caching"></span><h1>Server-side Caching<a class="headerlink" href="#server-side-caching" title="Permalink to this headline">¶</a></h1>
<div class="section" id="metadata-caching">
<h2>Metadata Caching<a class="headerlink" href="#metadata-caching" title="Permalink to this headline">¶</a></h2>
<p class="versionadded">
<span class="versionmodified">New in version 1.3.0.</span></p>
<p>Caching (or, rather, cache expiration) is always a difficult problem,
but it’s particularly vexing in Bcfg2 due to the number of different
data sources incorporated. In 1.3.0, we introduce some limited
caching of client metadata objects. Since a client metadata object
can be generated anywhere from 7 to dozens of times per client run
(depending on your templates), and since client metadata generation
was made more complex and powerful in 1.3.0, caching these objects
provides the easiest performance gain.</p>
<p>To enable caching, add a <tt class="docutils literal"><span class="pre">[caching]</span></tt> section to bcfg2.conf with a
client_metadata option containing one of the following modes:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">off</span></tt>: No caching of client metadata objects is performed. This
is the default.</li>
<li><tt class="docutils literal"><span class="pre">initial</span></tt>: Only initial metadata objects are cached. Initial
metadata objects are created only from the data in the
<a class="reference internal" href="plugins/grouping/metadata.html#server-plugins-grouping-metadata"><em>Metadata</em></a> plugin, before additional
groups from other plugins are merged in.</li>
<li><tt class="docutils literal"><span class="pre">cautious</span></tt>: Final metadata objects are cached, but each client’s
cache is cleared at the start of each client run, immediately after
probe data is received. Cache is also cleared as in <tt class="docutils literal"><span class="pre">aggressive</span></tt>
mode. <tt class="docutils literal"><span class="pre">on</span></tt> is a synonym for <tt class="docutils literal"><span class="pre">cautious</span></tt>.</li>
<li><tt class="docutils literal"><span class="pre">aggressive</span></tt>: Final metadata objects are cached. Each plugin is
responsible for clearing cache when appropriate.</li>
</ul>
<p>These are presented roughly in ascending order of speed, and
descending order of reliability. That is, odds are higher that
<tt class="docutils literal"><span class="pre">aggressive</span></tt> mode will result in stale data, but it gives the
biggest speed boost. <tt class="docutils literal"><span class="pre">off</span></tt> will never result in stale data, but it
gives no speed boost.</p>
<p>In addition to the <a class="reference internal" href="plugins/grouping/metadata.html#server-plugins-grouping-metadata"><em>Metadata</em></a> plugin,
Bcfg2 includes three plugins that can set additional groups, and thus
may affect the caching behavior. They are
<a class="reference internal" href="plugins/grouping/grouppatterns.html#server-plugins-grouping-grouppatterns"><em>GroupPatterns</em></a>,
<a class="reference internal" href="plugins/probes/index.html#server-plugins-probes-index"><em>Probes</em></a>, and
<a class="reference internal" href="plugins/connectors/puppetenc.html#server-plugins-connectors-puppetenc"><em>PuppetENC</em></a>. All of those plugins
<strong>except</strong> for PuppetENC fully support all caching levels. PuppetENC
is incompatible with <tt class="docutils literal"><span class="pre">aggressive</span></tt>, and may result in some stale data
with <tt class="docutils literal"><span class="pre">cautious</span></tt>.</p>
<p>If you are not using the PuppetENC plugin, and do not have any custom
plugins that provide additional groups, then all four modes should be
safe to use. If you are using PuppetENC or have custom Connector
plugins that provide additional groups, then you may want to start
with <tt class="docutils literal"><span class="pre">cautious</span></tt> or <tt class="docutils literal"><span class="pre">initial</span></tt>.</p>
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<li><a class="reference internal" href="#">Server-side Caching</a><ul>
<li><a class="reference internal" href="#metadata-caching">Metadata Caching</a></li>
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