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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Field caches — Whoosh 2.7.4 documentation</title> <link rel="stylesheet" href="_static/default.css" type="text/css" /> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '', VERSION: '2.7.4', COLLAPSE_INDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </script> <script type="text/javascript" src="_static/jquery.js"></script> <script type="text/javascript" src="_static/underscore.js"></script> <script type="text/javascript" src="_static/doctools.js"></script> <link rel="top" title="Whoosh 2.7.4 documentation" href="index.html" /> <link rel="next" title="Tips for speeding up batch indexing" href="batch.html" /> <link rel="prev" title="“Did you mean... ?” Correcting errors in user queries" href="spelling.html" /> </head> <body> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="batch.html" title="Tips for speeding up batch indexing" accesskey="N">next</a> |</li> <li class="right" > <a href="spelling.html" title="“Did you mean... ?” Correcting errors in user queries" accesskey="P">previous</a> |</li> <li><a href="index.html">Whoosh 2.7.4 documentation</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="field-caches"> <h1>Field caches<a class="headerlink" href="#field-caches" title="Permalink to this headline">¶</a></h1> <p>The default (<tt class="docutils literal"><span class="pre">filedb</span></tt>) backend uses <em>field caches</em> in certain circumstances. The field cache basically pre-computes the order of documents in the index to speed up sorting and faceting.</p> <p>Generating field caches can take time the first time you sort/facet on a large index. The field cache is kept in memory (and by default written to disk when it is generated) so subsequent sorted/faceted searches should be faster.</p> <p>The default caching policy never expires field caches, so reused searchers and/or sorting a lot of different fields could use up quite a bit of memory with large indexes.</p> <div class="section" id="customizing-cache-behaviour"> <h2>Customizing cache behaviour<a class="headerlink" href="#customizing-cache-behaviour" title="Permalink to this headline">¶</a></h2> <p>(The following API examples refer to the default <tt class="docutils literal"><span class="pre">filedb</span></tt> backend.)</p> <p><em>By default</em>, Whoosh saves field caches to disk. To prevent a reader or searcher from writing out field caches, do this before you start using it:</p> <div class="highlight-python"><div class="highlight"><pre><span class="n">searcher</span><span class="o">.</span><span class="n">set_caching_policy</span><span class="p">(</span><span class="n">save</span><span class="o">=</span><span class="bp">False</span><span class="p">)</span> </pre></div> </div> <p>By default, if caches are written to disk they are saved in the index directory. To tell a reader or searcher to save cache files to a different location, create a storage object and pass it to the <tt class="docutils literal"><span class="pre">storage</span></tt> keyword argument:</p> <div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">whoosh.filedb.filestore</span> <span class="kn">import</span> <span class="n">FileStorage</span> <span class="n">mystorage</span> <span class="o">=</span> <span class="n">FileStorage</span><span class="p">(</span><span class="s">"path/to/cachedir"</span><span class="p">)</span> <span class="n">reader</span><span class="o">.</span><span class="n">set_caching_policy</span><span class="p">(</span><span class="n">storage</span><span class="o">=</span><span class="n">mystorage</span><span class="p">)</span> </pre></div> </div> </div> <div class="section" id="creating-a-custom-caching-policy"> <h2>Creating a custom caching policy<a class="headerlink" href="#creating-a-custom-caching-policy" title="Permalink to this headline">¶</a></h2> <p>Expert users who want to implement a custom caching policy (for example, to add cache expiration) should subclass <tt class="xref py py-class docutils literal"><span class="pre">whoosh.filedb.fieldcache.FieldCachingPolicy</span></tt>. Then you can pass an instance of your policy object to the <tt class="docutils literal"><span class="pre">set_caching_policy</span></tt> method:</p> <div class="highlight-python"><div class="highlight"><pre><span class="n">searcher</span><span class="o">.</span><span class="n">set_caching_policy</span><span class="p">(</span><span class="n">MyPolicy</span><span class="p">())</span> </pre></div> </div> </div> </div> </div> </div> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h3><a href="index.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">Field caches</a><ul> <li><a class="reference internal" href="#customizing-cache-behaviour">Customizing cache behaviour</a></li> <li><a class="reference internal" href="#creating-a-custom-caching-policy">Creating a custom caching policy</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="spelling.html" title="previous chapter">“Did you mean... ?” Correcting errors in user queries</a></p> <h4>Next topic</h4> <p class="topless"><a href="batch.html" title="next chapter">Tips for speeding up batch indexing</a></p> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="_sources/fieldcaches.txt" rel="nofollow">Show Source</a></li> </ul> <div id="searchbox" style="display: none"> <h3>Quick search</h3> <form class="search" action="search.html" method="get"> <input type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> <p class="searchtip" style="font-size: 90%"> Enter search terms or a module, class or function name. </p> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="batch.html" title="Tips for speeding up batch indexing" >next</a> |</li> <li class="right" > <a href="spelling.html" title="“Did you mean... ?” Correcting errors in user queries" >previous</a> |</li> <li><a href="index.html">Whoosh 2.7.4 documentation</a> »</li> </ul> </div> <div class="footer"> © Copyright 2007-2012 Matt Chaput. 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