Nginx + PHP FASTCGI FAILS - how to debug ?

[Usu]

Hi, thanks for the replys.

ulimit output: unilimited
To run dstat I will have to wait until php becomes unresponsive, it could be hours or days, I can't reproduce it since it's not releated to the load on the server, I tried stressing it with Apache Benchmark but even with all the cpus at 100% the site was still working fine (only slow), I use munin and every time it happens I don't see any weird behavior apart form the mysql threads that have a spike.

PHP_FCGI_MAX_REQUESTS = 500
I'm using dynamic child with php-fpm (but I've already tried many setting here even without php-fpm)

Here's the first part of the nginx configuration, let me know if you need the whole thing

user       www-data www-data;
worker_processes  12;
error_log  logs/error.log;
pid        /dev/shm/nginx.pid;
worker_rlimit_nofile 10000;

events {
    worker_connections  1024;
    use epoll;
}

http {
    include    mime.types;
   #include    /etc/nginx/proxy.conf;
    include    /usr/local/nginx/conf/fastcgi_params;

    default_type application/octet-stream;

     log_format   main '$remote_addr - $remote_user [$time_local] "$request" '
                       '$status $body_bytes_sent "$http_referer" '
                       '"$http_user_agent" "$http_x_forwarded_for"';

    access_log   logs/access.log  main;
    sendfile     on;
    tcp_nopush   on;
    server_names_hash_bucket_size 128; # this seems to be required for some vhosts
    client_max_body_size 12m;
    large_client_header_buffers 8 32k;

    # output compression saves bandwidth
    gzip              on;
    gzip_proxied      any;
    gzip_http_version 1.1;
    #gzip_min_length  1100;
    gzip_comp_level   2;
    #gzip_buffers     4 8k;
    gzip_types        text/plain text/css application/x-javascript text/xml application/xml application/xml+rss text/javascript application/atom+xml;
    #gzip_vary        on;
    #gzip_disable     "MSIE [1-6]\.";

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,40332,71034#msg-71034