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<p>This text is a work in progress—highly subject to
change—and may not accurately describe any released
version of the Apache™ Subversion® software.
Bookmarking or otherwise referring others to this page is
probably not such a smart idea. Please visit
<a href="http://www.svnbook.com/">http://www.svnbook.com/</a>
for stable versions of this book.</p>
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<table width="100%" summary="Navigation header">
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<th colspan="3" align="center">Server Optimization</th>
</tr>
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<td width="20%" align="left"><a accesskey="p" href="svn.serverconfig.operational-logging.html">Prev</a> </td>
<th width="60%" align="center">Chapter 6. Server Configuration</th>
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<div class="sect1" title="Server Optimization">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="svn.serverconfig.optimization"></a>Server Optimization</h2>
</div>
</div>
</div>
<p>Part of the due diligence when offering a service such as a
Subversion server involves capacity planning and performance
tuning. Subversion doesn't tend to be particularly greedy in
terms of server resources such as CPU cycles and memory, but any
service can benefit from optimizations, especially when usage of
the service skyrockets<sup>[<a id="idp17016096" href="#ftn.idp17016096" class="footnote">75</a>]</sup>. In this section, we'll discuss
some ways you can tweak your Subversion server configuration
to offer even better performance and scalability.</p>
<div class="sect2" title="Data Caching">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.serverconfig.optimization.caching"></a>Data Caching</h3>
</div>
</div>
</div>
<p>Generally speaking, the most expensive part of a
Subversion server's job is fetching data from the repository.
Subversion 1.6 attempted to offset this cost by introducing
some in-memory caching of certain classes of data read from
the repository. But Subversion 1.7 takes this a step further,
not only caching the results of some of the more costly
operations, but also by providing in each of the available
servers the means by which fine-tune the size and some
behaviors of the cache.</p>
<p>For <span class="command"><strong>svnserve</strong></span>, you can specify the size
of the cache using the <code class="option">--memory-cache-size</code>
(<code class="option">-M</code>) command-line option. You can also
dictate whether <span class="command"><strong>svnserve</strong></span> should attempt to
cache content fulltexts and deltas via the
boolean <code class="option">--cache-fulltexts</code>
and <code class="option">--cache-txdeltas</code> options,
respectively.</p>
<div class="informalexample">
<pre class="screen">
$ svnserve -d -r /path/to/repositories \
--memory-cache-size 1024 \
--cache-txdeltas yes \
--cache-fulltexts yes
…
$
</pre>
</div>
<p><span class="command"><strong>mod_dav_svn</strong></span> provides the same degree of
cache configurability via <code class="filename">httpd.conf</code>
directives.
The <code class="literal">SVNInMemoryCacheSize</code>,
<code class="literal">SVNCacheFullTexts</code>,
and <code class="literal">SVNCacheTextDeltas</code> directives may be
used at the server configuration level to control Subversion's
data cache characteristics:</p>
<div class="informalexample">
<pre class="programlisting">
<IfModule dav_svn_module>
# Enable a 1 Gb Subversion data cache for both fulltext and deltas.
SVNInMemoryCacheSize 1048576
SVNCacheTextDeltas On
SVNCacheFullTexts On
</IfModule>
</pre>
</div>
<p>So what settings should you use? Certainly you need to
consider what resources are available on your server. To get
any benefit out of the cache at all, you'll probably want to
let the cache be at least large enough to hold all the files
which are most commonly accessed in your repository (for
example, your project's <code class="filename">trunk</code> directory
tree).</p>
<div class="tip" title="Tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Tip]" src="images/tip.png" />
</td>
<th align="left">Tip</th>
</tr>
<tr>
<td align="left" valign="top">
<p>Setting the memory cache size to <code class="literal">0</code>
will disable this enhanced caching mechanism and cause
Subversion to fall back to using the older cache mechanisms
introduced in Subversion 1.6.</p>
</td>
</tr>
</table>
</div>
<div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Note]" src="images/note.png" />
</td>
<th align="left">Note</th>
</tr>
<tr>
<td align="left" valign="top">
<p>Currently, only repositories which make use of the FSFS
backend data store make use of this data caching
functionality.</p>
</td>
</tr>
</table>
</div>
</div>
<div class="sect2" title="Network Compression of Data">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.serverconfig.optimization.compression"></a>Network Compression of Data</h3>
</div>
</div>
</div>
<p>Compressing the data transmitted across the wire can
greatly reduce the size of those network transmissions, but
comes at the cost of server (and client) CPU cycles.
Depending on your server's CPU capacity, the typical access
patterns of the clients who use your servers, and the
bandwidth of the networks between them, you might wish to fine
tune just how hard your server will work to compress the data
it sends across the wire. To assist with this fine tuning
process, Subversion 1.7 offers
the <code class="option">--compression</code> (<code class="option">-c</code>)
option to <span class="command"><strong>svnserve</strong></span> and
the <code class="literal">SVNCompressionLevel</code> directive
for <span class="command"><strong>mod_dav_svn</strong></span>. Both accept a value which
is an integer between 0 and 9 (inclusive), where 9 offers the
best compression of wire data, and 0 disables compression
altogether.</p>
<p>For example, on a local area network (LAN) with 1-Gigabit
connections, it might not make sense to have the server
compress its network transmissions (which also forces the
clients to decompress them), as the network itself is so fast
that users won't really benefit from the smaller overall
network payload. On the other hand, servers which are
accessed primarily by clients with low-bandwidth connections
would be doing those clients a favor by minimizing the overall
size of its network communications.</p>
</div>
<div class="footnotes">
<br />
<hr width="100" align="left" />
<div class="footnote">
<p><sup>[<a id="ftn.idp17016096" href="#idp17016096" class="para">75</a>] </sup>In Subversion's case, the
skyrocketing affect is, of course, due to its cool name. Well,
that and its popularity, reliability, ease of
use….</p>
</div>
</div>
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<p>You are reading <em>Version Control with Subversion</em> (for
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and C. Michael Pilato.</p>
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