I upgraded Wordpress on my huge blog (around 300 000 visitors per day) from 2.8.4 to latest 3.3.2. Everything went well but my server started returning lot of Errors 502 although it worked perfectly fine before.
It's running php-fpm & nginx with varnish caching, so this probably means problems talking to the backend, e.g. php-fpm. Did someone have similar experience and what's possible to do about it? Which settings should I adjust? I can't increase the memory limits too much coz the load is pretty high already but it was perfectly stable before the upgrade...
16 children in php-fpm config, xeon, 8gb ram, ssd, ubuntu
nginx error log is full of this:
2012/05/22 18:38:17 [error] 3643#0: *113267 connect() to unix:/var/run/php5-fpm.sock failed (11: Resource temporarily unavailable) while connecting to upstream, client: 22.214.171.124, server: site.com, request: "GET / HTTP/1.1", upstream: "fastcgi://unix:/var/run/php5-fpm.sock:", host: "www.site.com"
php log is ok, nothing unusual, just these exit messages caused probably by reaching max amount of requests:
May 22 18:48:47.058006 [NOTICE] [pool www] child 9509 exited with code 0 after 253.130628 seconds from start May 22 18:48:47.058913 [NOTICE] [pool www] child 9591 started
seems there is some space for using more RAM:
free -m total used free shared buffers cached Mem: 8001 3973 4028 0 70 3271 -/+ buffers/cache: 631 7369 Swap: 2534 0 2534