<!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>Concurrency, locking, and versioning — Whoosh 2.5.7 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: '2.5.7',
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 2.5.7 documentation" href="index.html" />
<link rel="next" title="Indexing and searching document hierarchies" href="nested.html" />
<link rel="prev" title="Tips for speeding up batch indexing" href="batch.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="nested.html" title="Indexing and searching document hierarchies"
accesskey="N">next</a> |</li>
<li class="right" >
<a href="batch.html" title="Tips for speeding up batch indexing"
accesskey="P">previous</a> |</li>
<li><a href="index.html">Whoosh 2.5.7 documentation</a> »</li>
</ul>
</div>
<div class="document">
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body">
<div class="section" id="concurrency-locking-and-versioning">
<h1>Concurrency, locking, and versioning<a class="headerlink" href="#concurrency-locking-and-versioning" title="Permalink to this headline">¶</a></h1>
<div class="section" id="concurrency">
<h2>Concurrency<a class="headerlink" href="#concurrency" title="Permalink to this headline">¶</a></h2>
<p>The <tt class="docutils literal"><span class="pre">FileIndex</span></tt> object is “stateless” and should be share-able between
threads.</p>
<p>A <tt class="docutils literal"><span class="pre">Reader</span></tt> object (which underlies the <tt class="docutils literal"><span class="pre">Searcher</span></tt> object) wraps open files and often
individual methods rely on consistent file cursor positions (e.g. they do two
<tt class="docutils literal"><span class="pre">file.read()</span></tt>s in a row, so if another thread moves the cursor between the two
read calls Bad Things would happen). You should use one Reader/Searcher per
thread in your code.</p>
<p>Readers/Searchers tend to cache information (such as field caches for sorting),
so if you can share one across multiple search requests, it’s a big performance
win.</p>
</div>
<div class="section" id="locking">
<h2>Locking<a class="headerlink" href="#locking" title="Permalink to this headline">¶</a></h2>
<p>Only one thread/process can write to an index at a time. When you open a writer,
it locks the index. If you try to open a writer on the same index in another
thread/process, it will raise <tt class="docutils literal"><span class="pre">whoosh.store.LockError</span></tt>.</p>
<p>In a multi-threaded or multi-process environment your code needs to be aware
that opening a writer may raise this exception if a writer is already open.
Whoosh includes a couple of example implementations
(<a class="reference internal" href="api/writing.html#whoosh.writing.AsyncWriter" title="whoosh.writing.AsyncWriter"><tt class="xref py py-class docutils literal"><span class="pre">whoosh.writing.AsyncWriter</span></tt></a> and <a class="reference internal" href="api/writing.html#whoosh.writing.BufferedWriter" title="whoosh.writing.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">whoosh.writing.BufferedWriter</span></tt></a>)
of ways to work around the write lock.</p>
<p>While the writer is open and during the commit, <strong>the index is still available
for reading</strong>. Existing readers are unaffected and new readers can open the
current index normally.</p>
<div class="section" id="lock-files">
<h3>Lock files<a class="headerlink" href="#lock-files" title="Permalink to this headline">¶</a></h3>
<p>Locking the index is accomplished by acquiring an exclusive file lock on the
<tt class="docutils literal"><span class="pre"><indexname>_WRITELOCK</span></tt> file in the index directory. The file is not deleted
after the file lock is released, so the fact that the file exists <strong>does not</strong>
mean the index is locked.</p>
</div>
</div>
<div class="section" id="versioning">
<h2>Versioning<a class="headerlink" href="#versioning" title="Permalink to this headline">¶</a></h2>
<p>When you open a reader/searcher, the reader represents a view of the <strong>current
version</strong> of the index. If someone writes changes to the index, any readers
that are already open <strong>will not</strong> pick up the changes automatically. A reader
always sees the index as it existed when the reader was opened.</p>
<p>If you are re-using a Searcher across multiple search requests, you can check
whether the Searcher is a view of the latest version of the index using
<a class="reference internal" href="api/searching.html#whoosh.searching.Searcher.up_to_date" title="whoosh.searching.Searcher.up_to_date"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.searching.Searcher.up_to_date()</span></tt></a>. If the searcher is not up to date,
you can get an up-to-date copy of the searcher using
<a class="reference internal" href="api/searching.html#whoosh.searching.Searcher.refresh" title="whoosh.searching.Searcher.refresh"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.searching.Searcher.refresh()</span></tt></a>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># If 'searcher' is not up-to-date, replace it</span>
<span class="n">searcher</span> <span class="o">=</span> <span class="n">searcher</span><span class="o">.</span><span class="n">refresh</span><span class="p">()</span>
</pre></div>
</div>
<p>(If the searcher has the latest version of the index, <tt class="docutils literal"><span class="pre">refresh()</span></tt> simply
returns it.)</p>
<p>Calling <tt class="docutils literal"><span class="pre">Searcher.refresh()</span></tt> is more efficient that closing the searcher and
opening a new one, since it will re-use any underlying readers and caches that
haven’t changed.</p>
</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="#">Concurrency, locking, and versioning</a><ul>
<li><a class="reference internal" href="#concurrency">Concurrency</a></li>
<li><a class="reference internal" href="#locking">Locking</a><ul>
<li><a class="reference internal" href="#lock-files">Lock files</a></li>
</ul>
</li>
<li><a class="reference internal" href="#versioning">Versioning</a></li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
<p class="topless"><a href="batch.html"
title="previous chapter">Tips for speeding up batch indexing</a></p>
<h4>Next topic</h4>
<p class="topless"><a href="nested.html"
title="next chapter">Indexing and searching document hierarchies</a></p>
<h3>This Page</h3>
<ul class="this-page-menu">
<li><a href="_sources/threads.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="nested.html" title="Indexing and searching document hierarchies"
>next</a> |</li>
<li class="right" >
<a href="batch.html" title="Tips for speeding up batch indexing"
>previous</a> |</li>
<li><a href="index.html">Whoosh 2.5.7 documentation</a> »</li>
</ul>
</div>
<div class="footer">
© Copyright 2007-2012 Matt Chaput.
Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
</div>
</body>
</html>
