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<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I use Varnish on four load-balanced web servers running Apache with several virtual hosts providing MediaWiki wikis. Last week I upgraded the web servers to support upgrading MediaWiki from 1.26 to 1.27 due to PHP requirements. This meant
upgrading (reinstalling) Ubuntu 12.04 to 16.04, meaning I went from PHP 5.3 to 7, Apache 2.4 + mod_php to Apache 2.4 + PHP-FPM, and Varnish 3 to 4.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">For the upgrade from Varnish 3 to 4, I adapted <a href="https://gist.github.com/Calygos/105957a997ea3bde6b8257a1f34bbd20">
my VCL code</a> accordingly, based on <a href="https://www.mediawiki.org/wiki/Manual:Varnish_caching">
Mediawiki Varnish sample code</a>, but for reasons I don’t understand, my Varnish hit ratio dropped from around 86% to ~20-37%.
<a href="http://imgur.com/jX4iu6s">This picture</a> shows a graph of the last 10 days hit ratio calculations for the four web servers. The graph is calculated using metrics from the Collectd Varnish plugin as (conns - bereqs / conns), i.e.:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas">asPercent(<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> diffSeries(<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> linux.<i>hostname</i>.varnish-default-connections.connections-received,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> linux.<i>hostname</i>.varnish-default-backend.http_requests-requests<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> ),<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> linux.<i>hostname</i>.varnish-default-connections.connections-received<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas">)<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve also tried the Varnish hit and miss metrics but those give similar results. So I’m not sure what changed to give such a poor hit ratio, despite otherwise good performance on large, busy wikis. It’s possible it could be something in
MediaWiki’s cookie and/or session handling and I’ve been investigating that possibility as well, but I figured this would be a good place to ask, too.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Justin<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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