Connections dropped under load

George Georgovassilis g.georgovassilis at
Wed Jan 12 00:33:14 CET 2011

On 11.01.2011 20:36, Ask Bjørn Hansen wrote:
> How can you limit the number of threads?   And why would you?
> I run Varnish under both Xen and KVM (and there's an instance on 32-bit linux!) - none of them have trouble with our small load (<1000 requests per second).   (And all very standard configurations).
>   - ask
Hi Ask,

Some background: The hosting plans that use paravirtualization (such as 
Virtuozzo) artificially limit some logical resources such as sockets, 
pages, virtual memory address space (which you cannot cheat your way out 
of by just creating more swap space) and number of processes. The latter 
is called "numproc" and has fairly low values. The dev plan for my 
project has several such virtual instances, which however don't allow 
more than 150 threads for more than 5 minutes. This is quite annoying, 
but a real business model and I have to accept that (just as I have to 
accept that varnish is a thread-fest) - even more annoying because both 
the memory and CPU reserves would otherwise be more than adequate to 
serve the application: during the stresstest I mentioned earlier Varnish 
is taking up a neglible 4% CPU load while doing some pretty elaborate 
pattern/cookie/locale matching and hashing (yeah, I have a big VCL).

I thank you all for your valuable input. The earlier posts delineate an 
accurate picture of where the limitations of using varnish on a 
constrained environment are. Several people use nginx/varnish cascades 
(apparently with keep-alive/pipelining) which is the next step I will be 
investigating. Thus - for my part - my questions have been answered and 
I'd like to close this topic.

Best regards,
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the varnish-misc mailing list