Hi Alexander, On Mon, Aug 16, 2010 at 12:02:47AM +0200, Alexander Staubo wrote: > On Wed, Aug 11, 2010 at 11:22 PM, Willy Tarreau <[email protected]> wrote: > >> We are seeing some requests taking a while before being able to get a > >> connection through to HAProxy. Using tcpdump we are seeing cases where > >> the clients needs 9 SYN packets before HAProxy responds to the > >> connect. Other services on the same box do not suffer the same > >> problem, so it's definitely HAProxy being overloaded. Is there > >> anything we can tune to improve the situation? > > > > When you observe this, it means that the SYN backlog queue is too short. > > Haproxy itself does not respond to SYN packets, it's the system which > > responds to SYN with a SYN-ACK, then when it gets the final ACK from the > > client, it wakes haproxy up. > [...] > > After a bit of debugging it seems that the problem is not on the > server end at all -- but with the ISP. :-/
Ouch... smells like an overloaded firewall then... > Thanks for the useful information, and thanks for trying to help -- > sorry to lead you on a wild goose chase. :-) No problem, and your tests once served to spot and fix a major queuing issue ;-) > >> The processor load is not very high (~3.3 among four cores), and we don't > >> see any obvioius bottlenecks. However, it is running Varnish as well. > > > > What else is running on the machine ? It does not seem possible to have > > that high a load with that little traffic ! Even my 5-year old notebook > > does not report any CPU usage at that load :-/ > > Rails. :-) Ah, one word explains it all :-) Cheers, Willy
