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<div class="section" id="logging-in-varnish">
<span id="users-guide-logging"></span><h1>Logging in Varnish<a class="headerlink" href="#logging-in-varnish" title="Permalink to this headline">ΒΆ</a></h1>
<p>One of the really nice features in Varnish is the way logging
works. Instead of logging to a normal log file Varnish logs to a shared
memory segment, called the VSL - the Varnish Shared Log. When the end
of the segment is reached we start over, overwriting old data.</p>
<p>This is much, much faster than logging to a file and it doesn't
require disk space. Besides it gives you much, much more information
when you need it.</p>
<p>The flip side is that if you forget to have a program actually write the
logs to disk they will be overwritten.</p>
<p><cite>varnishlog</cite> is one of the programs you can use to look at what Varnish
is logging. <cite>varnishlog</cite> gives you the raw logs, everything that is
written to the logs. There are other clients that can access the logs as well, we'll show you
these later.</p>
<p>In the terminal window you started Varnish now type <tt class="docutils literal"><span class="pre">varnishlog</span> <span class="pre">-g</span> <span class="pre">raw</span></tt>
and press enter.</p>
<p>You'll see lines like these scrolling slowly by.:</p>
<div class="highlight-python"><pre>0 CLI - Rd ping
0 CLI - Wr 200 19 PONG 1273698726 1.0</pre>
</div>
<p>These is the Varnish master process checking up on the caching process
to see that everything is OK.</p>
<p>Now go to the browser and reload the page displaying your web app.</p>
<p>You'll see lines like these.:</p>
<div class="highlight-python"><pre>11 SessOpen c 127.0.0.1 58912 :8080 0.0.0.0 8080 1273698726.933590 14
11 ReqStart c 127.0.0.1 58912
11 ReqMethod c GET
11 ReqURL c /
11 ReqProtocol c HTTP/1.1
11 ReqHeader c Host: localhost:8080
11 ReqHeader c Connection: keep-alive</pre>
</div>
<p>The first column is an arbitrary number, it identifies the
transaction. Lines with the same number are coming from the same
transaction. The second column is the <em>tag</em> of the log message. All
log entries are tagged with a tag indicating what sort of activity is
being logged.</p>
<p>The third column tell us whether this is is data coming from or going
to the client ('c'), or the backend ('b'). The forth column is the data
being logged.</p>
<p>Now, you can filter quite a bit with <cite>varnishlog</cite>. The basic options we think you
want to know are:</p>
<dl class="docutils">
<dt>'-b'</dt>
<dd>Only show log lines from traffic going between Varnish and the backend
servers. This will be useful when we want to optimize cache hit rates.</dd>
<dt>'-c'</dt>
<dd>Same as '-b' but for client side traffic.</dd>
<dt>'-g request'</dt>
<dd>Group transactions by request.</dd>
<dt>'-q query'</dt>
<dd>Only list transactions matching this query.</dd>
</dl>
<p>For more information on this topic please see <a class="reference internal" href="../reference/varnishlog.html#varnishlog-1"><em>varnishlog</em></a>.</p>
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