nginx reverse proxy proxies subset of requests slowly

[anonymous_coward]

I have now done exhaustive tests on a larger instance that yields higher
throughput (>1000 #/s). The  /proc/sys/net/ipv4/tcp_syncookies setting
seems to have an effect on how much this subset of requests hang (it's
worse with the setting enabled). I'm seeing "TCP: Possible SYN flooding
on port 80. Dropping request." (or "Sending cookies") in kern.log.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,222724,222760#msg-222760