Nginx + php-fpm Slow Response When Busy

[godius]

Hello im running a quad core 8GB machine with fast scsi drives with 64bit centos 5.

 

Now on that site i run a site that get about 750.000 unique visitors, and the site uses ajax intensively. every pageview uses about 15 ajax http requests. I used to run my site on apache, but because of the insanely high load i decided to move to nginx.

 

I have setup nginx with php-fpm, and it is running quite good, only when it gets really busy (around 25 pageviews per second), i sometimes notice that i have to wait a few seconds before the server sends a response. This only happens when its busy, so i think ive hit some kind of limit in nginx. It is probably possible to resolve this by changing a certain value somewhere.

 

The server load is always low, around 1. Below i have posted some of the settings i have already modified.

 

[b]nginx.conf[/b]
events {
    worker_connections  6000;
}
worker_processes  12;
sendfile            on;
tcp_nopush          on;
tcp_nodelay         on;
keepalive_timeout   10;
gzip            on;
gzip_comp_level 2;
gzip_proxied    any;
gzip_types    text/plain text/html text/css application/x-javascript text/xml application/xml application/xml+rss text/javascript;

 

 

[b]php-fpm.conf[/b]
<value name="max_children">3000</value>
<value name="StartServers">200</value>
<value name="MinSpareServers">600</value>
<value name="MaxSpareServers">2000</value>
<value name="request_terminate_timeout">10s</value>

 

before on apache my site used to get busier because it was able to handle up to 35 pageviews per second, now i never see it go over 25, because i think nginx can not handle more with my current setup.

 

Please advice how to tune/optimize/improve my settings.

 

Kind regards,

 

Godius