Hey, we run a website of fairly decent volume.. up to nearly 4m pageviews a day.

At the moment we run a single machine with nginx and mysql and two worker machines with memcached and tornado instances. The nginx server is a reverse proxy to the workers and also serves static media.

The CPU load and memory usage on both of the worker boxes are well within reasonable expectations.

What I am observing is that nginx gets to about 320 requests per second then requests start backing up. Sometimes taking the server down, see this image: http://dl.dropbox.com/u/367355/nginx.png

When the server doesn't go down, we see a flattening of requests around the 320 mark, and the number of "waiting" requests and the memory usage of nginx spikes considerably.

I've tried upping the number of workers in case all of them are blocking for long enough to cause this cascading effect (the tornado db driver is not async) but didn't really see an improvement by adding more. I've also added lots of async memcached access to avoid hitting the db too much.

I've included the configs below.. thanks for any help you may have!

[code]
user www-data;
worker_processes 4;
worker_rlimit_nofile 32768;


error_log /dev/null crit;
pid /var/run/nginx.pid;

events {
worker_connections 8192;
use epoll;
}

http {
include /etc/nginx/mime.types;
default_type application/octet-stream;

access_log /dev/null;

sendfile on;

keepalive_timeout 0;
tcp_nodelay on;

gzip on;
gzip_types text/css text/plain text/javascript application/x-javascript application/json;
gzip_comp_level 5;
gzip_disable "msie6";

include /etc/nginx/conf.d/*.conf;
include /etc/nginx/sites-enabled/*;
}

[/code]


[code]
upstream bar {
server worker1:8888 max_fails=1 fail_timeout=10s;
server worker2:8888 max_fails=1 fail_timeout=10s;
}


server { # simple reverse-proxy
listen 80;
server_name bar.net;
#access_log logs/bar.access.log;
access_log /dev/null;


location /nginx_status {
stub_status on;
access_log off;
allow 127.0.0.1;
deny all;
}

location ^~ /static/ {
root /home/foo/bar;
if ($query_string) {
expires max;
}
}

# pass requests for dynamic content to tornado
location / {
proxy_pass_header Server;
proxy_set_header Host $http_host;
proxy_redirect false;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Scheme $scheme;
proxy_pass http://tweete;
}
error_page 411 /411.html;
location = /411.html {
root /home/foo/bar/static/error;
}

error_page 500 502 503 504 /500.html;
location = /500.html {
root /home/foo/bar/static/error;
}
}

[/code]