[Varnish] #188: thread pileup

Varnish varnish-bugs at projects.linpro.no
Fri Jan 11 18:44:57 CET 2008

#188: thread pileup
 Reporter:  steinove  |        Owner:  phk     
     Type:  defect    |       Status:  assigned
 Priority:  high      |    Milestone:          
Component:  varnishd  |      Version:  1.1.1   
 Severity:  normal    |   Resolution:          
 Keywords:            |  
Comment (by 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.

Ticket URL: <http://varnish.projects.linpro.no/ticket/188#comment:5>
Varnish <http://varnish.projects.linpro.no/>
The Varnish HTTP Accelerator

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