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. :-/ Thanks for the useful information, and thanks for trying to help -- sorry to lead you on a wild goose chase. :-) >> 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. :-)
