Hi,
I made an interesting observation using webservers (not just mongrel) under
red hat enterprise
linux ES release 4 (Nahant Update 5). Maybe this is helpful or somebody with
deeper networking
expertise can comment on this.
Once client said that 1-2% of the response of our server were unacceptably slow
(really huge 3s-21s).
So I did more ab and httperf tests and notice that very few requests do take a
very long time. Being clueless
I first thought that the ruby garbage collector or mongrel is causing the
effect, so after looking
at a similar setup using erlang's yaws or nginx alone, I noticed that sometimes
this can happen,
especially when increasing the number of concurrent connects to a large number
(e.g. 250-500).
I did the same on OS-X and did not notice these outliers.
After a lot of painful searching by luck we found one cure: inet_peer_threshold
was too small.
Chaging it to a much larger value made the problem go away.
echo 500000 > /proc/sys/net/ipv4/inet_peer_threshold
There is a trade-off here. A too small value causes too many delays from
inet-peer-storage cleaning
and a too big value makes life well for some limited time, but when it hits
you, it becomes really expensive.
Did you ever see this?
Thanks,
-Armin
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