nginx proxy being slow

[imran_k]

We are trying to act as a proxy for a site within the same DMZ. Things seem
to work fine, except when there is quite a heavy load. There are many CSS
assets that just hang upon retrieval. Sometimes the full page comes through;
sometimes just spins forever. 

Server: nginx 1.6.1 running on Linux. 
Memory: 18Gb

proxy_buffering on;
proxy_buffers 256 8k;
proxy_busy_buffers_size 64;
proxy_temp_file_write_size 64;

Under heavy loads, about 1500 requests a second, a page is not completely
sent back to the browser as some of the CSS resources taking anywhere from 2
- 10 seconds to return. It will just spin until eventually it gets sent
back. CPU and memory usage is not dramatically high. Smaller sites return
without any issue at all. 

Do I have the buffering wrong or is there something else at play?

Thank you

Imran

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,253796,253796#msg-253796