Need help: Varnish unexpectedly flushing cache weekly

[Joshua Levine]

Hi Jordi!

Been a while… :)

We have definitely seen the issue, though I am happy to say it has been months since the last time.

I recommend that you start with a look at SESS_WORKSPACE, default is 8192, but we set this to 32768 as we were seeing crashes:

# http://varnish.projects.linpro.no/ticket/364
# http://varnish.projects.linpro.no/ticket/391

The 32768 matches what we have set as the max on our load balancers as well as in our http profile.

Cheers,
Joshua


On Aug 24, 2011, at 9:09 AM, Jordi Salvat wrote:

> Hi,
> 
> we restarted our Varnish instance on Sunday 7th around 19:00.
> 
> On Wednesday 10th 9:45 the child process restarted (causes unknown) -- loosing the existing cache.
> 
> ... the cache slowly grew again ....
> 
> On Wednesday 17th around 2:00, the cache was somehow flushed, loosing about 75% of its objects.
> 
> ... the cache slowly grew again ....
> 
> On Wednesday 24th at 2:00, the cache was flushed again, loosing about 85% of its objects.
> 
> On each of these occasions our cache hit rate went down from ~90% to under 50%. Needless to say this is highly undesirable.
> 
> What might be causing this behaviour? Any hints and directions helping research welcome.
> 
> Thanks.
> 
> More details:
> 
> Varnish version: 2.1.5 (Debian lenny package 2.1.5-1~lenny4)
> O.S.: Linux s229-161 2.6.38 #1 SMP Sat Mar 26 09:51:44 CET 2011 x86_64 GNU/Linux
> 
> MRTG daily graphs for cache size and objects in cache:
> 
> <varnish_cache-day.png>
> 
> <varnish_objects-day.png>
> 
> Note how the two graphs are slightly different: size goes down between 2:00 and 15:30, object count goes down suddenly at 15:30.
> 
> Main VCL file attached (long to read -- feel free to ask questions).
> 
> -- 
> Jordi Salvat i Alabart
> CTO & Project Manager
> Salir.com
> +34 676 49 86 00
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