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<li class="toctree-l2 current"><a class="current reference internal" href="">Transactional file locking</a></li>
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<div class="section" id="transactional-file-locking">
<h1>Transactional file locking<a class="headerlink" href="#transactional-file-locking" title="Permalink to this headline">¶</a></h1>
<p>Nextcloud’s Transactional File Locking mechanism locks files to avoid
file corruption during normal operation. It performs these functions:</p>
<ul class="simple">
<li>Operates at a higher level than the filesystem, so you don’t need to use a
filesystem that supports locking</li>
<li>Locks parent directories so they cannot be renamed during any activity on
files inside the directories</li>
<li>Releases locks after file transactions are interrupted, for
example when a sync client loses the connection during an upload</li>
<li>Manages locking and releasing locks correctly on shared files during changes
from multiple users</li>
<li>Manages locks correctly on external storage mounts</li>
<li>Manages encrypted files correctly</li>
</ul>
<p>What Transactional File locking is not for: it will not prevent multiple users
from editing the same document, or give notice that other users are working on
the same document. Multiple users can open and edit a file at the same time and
Transactional File locking does not prevent this. Rather, it prevents
simultaneous file saving.</p>
<p>File locking is enabled by default, using the database locking backend. This
places a significant load on your database. Using <code class="docutils literal"><span class="pre">memcache.locking</span></code> relieves
the database load and improves performance. Admins of Nextcloud servers with
heavy workloads should install a memcache. (See
<a class="reference internal" href="../configuration_server/caching_configuration.html"><em>Configuring memory caching</em></a>.)</p>
<p>To use a memcache with Transactional File Locking, you must install the Redis
server and corresponding PHP module. After installing Redis you must enter a
configuration in your <code class="docutils literal"><span class="pre">config.php</span></code> file like this example:</p>
<div class="highlight-python"><div class="highlight"><pre>'filelocking.enabled' => true,
'memcache.locking' => '\OC\Memcache\Redis',
'redis' => array(
'host' => 'localhost',
'port' => 6379,
'timeout' => 0.0,
'password' => '', // Optional, if not defined no password will be used.
),
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">For enhanced security it is recommended to configure Redis to require
a password. See <a class="reference external" href="http://redis.io/topics/security">http://redis.io/topics/security</a> for more information.</p>
</div>
<p>If you want to configure Redis to listen on an Unix socket (which is
recommended if Redis is running on the same system as Nextcloud) use this example
<code class="docutils literal"><span class="pre">config.php</span></code> configuration:</p>
<div class="highlight-python"><div class="highlight"><pre>'filelocking.enabled' => true,
'memcache.locking' => '\OC\Memcache\Redis',
'redis' => array(
'host' => '/var/run/redis/redis.sock',
'port' => 0,
'timeout' => 0.0,
),
</pre></div>
</div>
<p>See <code class="docutils literal"><span class="pre">config.sample.php</span></code> to see configuration examples for Redis, and for all
supported memcaches.</p>
<p>If you are on Ubuntu you can follow <a class="reference external" href="https://www.techandme.se/how-to-configure-redis-cache-in-ubuntu-14-04-with-owncloud/">this guide</a> for a complete installation from scratch.</p>
<p>Learn more about Reds at <a class="reference external" href="http://redis.io/">Redis</a>. Memcached, the popular
distributed memory caching system, is not suitable for the new file locking
because it is not designed to store locks, and data can disappear from the cache
at any time. Redis is a key-value store, and it guarantees that cached objects
are available for as long as they are needed.</p>
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