Fatal error: Out of memory, but I do have plenty of memory (PHP)

Question

Since my question is getting longer and longer, I decide to re-write the whole question to make it better and shorter.

I run my website on dedicated server with 8GB

Answer 1

Try to run php over fcgid, this may help:

These are the classic errors you will see when running PHP as an Apache module. We struggled with these errors for months. Switching to using PHP via mod_fcgid (as James recommends) will fix all of these problems. Be sure you have the latest Visual C++ Redistributable package installed:

http://support.microsoft.com/kb/2019667

Also, I recommend switching to the 64-bit version of MySQL. No real reason to run the 32-bit version anymore.

Source: Apache 2.4.6.0 crash due to a problem in php5ts.dll 5.5.1.0