System can't take more than 5k req /sec

Jorge jnerin at
Sat Apr 26 12:33:24 CEST 2014

5k req/s is very low, I was able to achieve ~12-16k with a vm with 2 cores
and 8Gb, albeit our hit ratio was higher, around 90% (and it was a stress

One of the things I had to disable for our test was an iptables rule for
max new connections per second that we had to avoid some ddos, check to see
if you have some external limiting factor like that.

On Sat, Apr 26, 2014 at 4:10 AM, Jason Price <japrice at> wrote:

> Note: this isn't a varnish question, per se, because varnish indicates it
> isn't the problem.
> What OS parameters has the community found valuable to tweak?
> Varnish 3.0.5, running on a c3.4xlarge amazon instance.  16 'cores', 30gb
> ram, amazon linux (aka RHEL 6ish) and half of a 10gb card to play with.
>  Very recent linux kernel.
> We see approximately 50% cache hit.  Payload is approximately 3.5kBytes
> compressed.  Response times are averaging 10 milliseconds... Backend
> response time is around 17-20 milliseconds.  We aren't seeing any lru_nuked
> objects, so the cache is sized appropriately for the cachability of the
> data (we can only cache for 15ish minutes due to the nature of the data).
> Threads set to 4k per thread pool.  Two thread pools, increased
> sess-workspace.  I see queued messages in varnish stat, but I never see
> dropped messages, and I don't see the thread count getting near max of 8k
> (usually hovers around 3300-3500).  We have a very high requests to
> connections ratio (approximately 100:1).
> Vmod for url coding is in play, and occasionally some syslog messages.
> Tcp socket reuse and recycle got us some improvement.  I've also played
> with the txqueuelen on the network interface, and a couple other related
> parameters to little avail.
> Anything I can do?
> -Jason
> _______________________________________________
> varnish-misc mailing list
> varnish-misc at

Jorge Nerín
<jnerin at>
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