================================================================ I finally found the reason with oprofile. It was because the routing cache of Symfony. We have lots of pages with different urls and symfony caches them in one file (serialized data). So the cache file grows large and it needs more CPU to serialize and unserialize data.
Everything went well after I disabled the routing cache
We have three web servers with LVS (Apache 2.11 + PHP 5.26), and we use Symfony 1.0 for our products development.
But recently we have updated our products with Symfony 1.2.7 and we got a critical performance issue.
We use Ganglia to monitor our servers. Before the updates, the average load of web servers is under 1. After the updates, the load increases dramatically with load 80 at top (I can see CPU usage increases much from Ganglia).
I can't find the reasons. Is it because the Symfony framework? (But according to Ganglia, the load shouldn't increase so rapidly).
By the way, in our new products lots of AJAX are used, which means there are at least 5-7 PHP requests to open one page. Is this the reason?
Can anyone help me to find all the possible reasons? Or what else information should I offer to diagnose?
Thanks in advance and looking forward to your reply~