Things to know..
- memory_limit of PHP running as an Apache module
- MaxClients configuration option for Apache
- If MaxClients = 100, Server RAM = 2000 MB then memory_limit (should be) < 20 MB (?? => 20MB * 100 clients = 2000 MB (or 2 GB))
- This doesn't include other processes of the server, such as MySQL, Apache etc
- This example assume, each PHP is using max value 20 MB for all.
- More details and other explanations at the best answer - http://stackoverflow.com/questions/1425138/#answer-1425182