max clients != worker processes * worker connections

davidcie nginx-forum at
Tue Oct 11 15:02:34 UTC 2011


I relise that it may have been hammered on quite a few times already,
but I cannot understand the results I'm getting. I have a rather basic
setup on Ubuntu Server 11.04, where nginx (run as root) spawns 2
worker_processes and serves a basic HTML page. Each of these processes
should have its worker_connections set to 8192. There's no limit_zone
defined. worker_rlimit_nofile is set to 65536, keepalive_timeout 5.

Verifying max load, I run ab from another server on the subnet. It works
fine with "ab -kc 8000 -n 16000". However, when I do
"ab -kc 10000 -n 16000", ab shows about 3486 failed
requests in its results (Length: 1743, Exceptions: 1743), while nginx's
error.log features numerous "2011/10/11 16:49:24 [alert] 12081#0: 8192
worker_connections are not enough" errors. 

Testing a number of settings, it seems that there's a close to 1-1
relationship between worker_connections and the maximum concurrency
parameter to ab that doesn't produce errors. I tried setting
worker_processes to some high number (like 16), but it seems to have no
effect whatsoever.

Can you please let me know why this setup might not be serving the
"promised" ;-) worker_processes * worker_connections connections? Is it
possible that new connections are not being evenly distributed to the
two processes? Apologies if this is some basic error on our side, we're
still learing (and admiring) nginx and are more used to IIS!

Kind regards,
Dawid Ciecierski

Posted at Nginx Forum:,216517,216517#msg-216517

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