Hi, I'm having the same problem for a few weeks now, after x hours/days php becomes unresponsive, I've already changed 2 different php-fastcgi spawning scripts and tried php-fpm as well, switched between many version of the php 5.2 and 5.3 branches but the problem still remains so I don't think it's a php issue even if that would be the most logical conclusion.

When php becomes unresponsive (502 bad gateway error) all the php-cgi/php-fpm processes are still running and I can see them in top/ps aux, when I restart php everything start to work again.

I don't know if it's releated, but while I was browsing this forum a few minutes ago I got the 502 error with the same behavior it has when it happens on my site, it lasted some minutes than someone took care of it. Also, take a look at this discussion: http://groups.google.com/group/highload-php-en/browse_thread/thread/a3809a50eba71a45 I think that this is a nginx bug, it would be nice if some developer could look into this, I could provide error logs and such if needed, just let me know, thanks!