Performance plateau when keepalives enabled

[Maxim Dounin]

Hello!

On Mon, Mar 08, 2010 at 11:30:52AM -0500, powderhound wrote:

[...]

> When I run the benchmark with keepalive_timeout 65, nginx is 
> very slow (5-20 seconds delay) to accept new connections as soon 
> as it reaches 1500 concurrent connections.  It plateaus here: it 
> completes all the requests but it never exceeds approximately 
> 1500 concurrent connections.
> 
> Is this normal?  Everywhere I read tells me to leave keepalive 
> on and it shouldn't make any difference in nginx.  So is this a 
> keepalive problem, or a problem handling >1500 concurrent 
> connections?  What should I look at to fix it?

Most likely you hit some network-related limit of your OS or some 
firewall inbetween.  Check if firewalls have enough number of 
state entries, your OS isn't limited by number of sockets, network 
buffers and so on.

Maxim Dounin