Need help: Varnish unexpectedly flushing cache weekly

[Jordi Salvat]

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:

[image: varnish_cache-day.png]

[image: 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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