apache httpd process be killed by kernel oom

Solution 1:

This means is that a request to allocate X amount of memory failed. So the Kenrel invoked the OOM killer which will terminates the highest memory consuming applications. System is out of physical and/or swap memory. What can be used as temporary fix, is to increase your swap size, till getting more RAM modules or capacity added to your server.

Also you most likely have configured Apache with mpm_prefork as an Apache module. This setup is slow and not thread safe. Modern web server setups use Apache with mpm_event. This will give you better performance, without eating up all your memory.