[Varnish] #188: thread pileup
Varnish
varnish-bugs at projects.linpro.no
Mon Jan 14 01:37:43 CET 2008
#188: thread pileup
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Reporter: steinove | Owner: phk
Type: defect | Status: assigned
Priority: high | Milestone:
Component: varnishd | Version: 1.1.1
Severity: normal | Resolution:
Keywords: |
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Comment (by frekri):
Replying to [comment:5 frekri]:
> Replying to [comment:1 phk]:
> > My best diagnosis, is that the backend is very slow for some
particular popular object.
> >
> > One thread picks it up from the backend and a LOT of requests gets
parked on the busy object until it comes back from the backend.
> >
> > Once it comes back, all the parked requests gets reinjected and causes
the thread explosion.
> >
> > Some kind of pacing algorithm is obviously called for, the trick is to
find one that doesn't need too many carefully tweaked numbers to work
generally and reliably.
> >
> > Thinking...
> >
> > /phk
>
> On Nettby.no varnish crash almost every day. We run 4 varnish servers.
After I read your post I moved all objects with high traffic to lighttpd
and objects with less traffic to varnish. In total these objects had a lot
of traffic.
>
> On each server we had 1100 hits/s before the last crash today. Before
the crash we had increased iowait, but hits and everything else were
normal.
Last described crash was because of to slow Swap Space(Disk). I have
reconfigured varnish to use less memory than available ram.
I was able to recreate the thread problem this weekend and I'm able to
crash varnish like Steinove described on purpose when I gave it enough
non-cached requests from our users.
Let us know when you have a patch and we will test it for you.
--
Ticket URL: <http://varnish.projects.linpro.no/ticket/188#comment:6>
Varnish <http://varnish.projects.linpro.no/>
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