Apache spawns bunch of php-cgi processes and they don't exit - webite hangs

Question

Out of the blue, apache started to not to respond when I tried to load my website. Website is based on Drupal just for the information. I checked server status by doing

service httpd status

and it showed out that apache is still running even though it isn't responding. The webite starts to load but never finishes loading and the browser screen is just white. After I restarted apache, it worked but crash happened again in like half of an hour. Further investigation showed that if I issue

ps auxwwf

there is bunch of php-cgi processes that are just there and never exit. If I run

killall php-cgi

the website starts to respond again. But it again hangs in about half of an hour. If I try to kill all php-cgi processes again, this doesn't solve the issue anymore and I have to restart the wole httpd.

Does anyone have the idea why this is happening, what could be the cause and how to fix this issue.

I am running CentOS 6 with Apache 2.2.27 and PHP 5.4.27. My website gets around 5000 unique visitors per day.

Answer 1

It showed out that the Drupals cache_form table in database was over 6GB big and therefore automatic clean stopped working. Whenever process wanted to access this database, the process php-cgi hung. After manually clearing the cache table, everything started to work just fine.