varnish 2.0.4 backend errors

Kristian Lyngstol kristian at
Tue Jul 14 12:05:00 CEST 2009

On Tue, Jul 14, 2009 at 11:46:58AM +0200, Lazy wrote:
> 2009/7/14 Kristian Lyngstol <kristian at>:
> > 6000 threads is too much. Since it's per pool, it'll cause up to 12 000
> > threads to start. That's not likely to go over all that well. If you have
> > that sort of traffic, you need to scale out. Also, 10 thread minimum is
> > pretty low.
> >
> > I typically recommend setting the minimum thread count to what you expect
> > your normal traffic to be at peak hours. It's probably a dedicated
> > machines, and idle threads have barely any overhead, while creating new
> > threads can take some time.
> at first i had 3000 threads set and varnish ocassionly droped
> connections, so I doubled it
> so what whould be a recomended values ?
> will -w 1024,1024 -p thread_pools=6 whould be ok ?

6 thread pools is overkill. And the number of threads is multiplied with
the thread pools, so in this case you're essentially writing -w 6k,6k... 

I'd advice something like -w 200,1200 -p thread_pools=2 to begin with. Just
watch the overflows in varnishstat (it'll increase a good bit during
startup since it takes a little time to create the 400 threads). It should
stay fairly static after startup.

> the site is usually not so busy, but it has sometimes spikes of static
> traffic (about 50Mbps) that's why i upped the thread limit, 3000 was
> to low

I seriously doubt 3k was too low. More likely, the min threads was hurting
you. Three thousand threads is quite a bit. Remember that these are actual
requests being handled, not keep-alive connections and the like.

> is it safe to change thread_pools on runtime ?

Safe; I'd assume so. But I don't know if it actually takes effect. I've yet
to see any good reason to change it from the default.

Kristian Lyngstøl
Redpill Linpro AS
Tlf: +47 21544179
Mob: +47 99014497
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