Apache limitting concurrent connections to 150

The answer is "it depends" -- things which it could depend upon:

1. Are you planning on using PHP with your Apache environment? If so then using the worker MPM might not be for you see this link as certain PHP modules aren't thread-safe.

2. Are you planning on performing operations which might require locking of files? If so then using the worker MPM might not be for you. Threads are not full POSIX processes and therefore don't necessarily obey file locking operations.

   An example of this is Subversion version < 1.5 - these versions made use of apr and apr-util libraries using Berkeley DB for performing commits. Berkeley DB relies upon locking therefore this could result in commits which corrupt your repositories

The key thing to do is to figure out what you're trying to do with your Apache service - how are you trying to serve things, how are the back-end processes operating to construct the data to be served.

• Are you just interfacing with a Tomcat service via mod_proxy or AJP? It's usually okay to go with the worker.
• Are you doing things with Apache modules (SVN, PHP are two examples)? In that case prefork might be safer.
• Are you using NFS (doesn't always support filesystem locking properly)? Again prefork probably the safer option.

YMMV - but ultimately you need to understand the architecture underlying things to make a true judgement call on this. If you don't understand the architecture then go with prefork as it's the safer route.

Optimizing memory footprint is usually done by reducing (and limiting) these factors:

• count of simultaneous Apache processes (I'd recommend switching to prefork MPM, which is kindof more controllable in memory-limited environs)
• moving away from mod_php or php_cgi to fastcgi, mod_cfgid works fine. Reducing the count of allowed spawned php processes by FcgidMaxProcesses and removing long timeouts (see http://httpd.apache.org/mod_fcgid/mod/mod_fcgid.html )
• server "threadiness", especially by reducing unnecessarily long timeouts ((dis)connect timeouts, keepalives, ...)

If the load is getting really heavy, you should also look into the speed of request handling (faster loading improve the total size*time of memory needed for one request)

• optimizing your website code (improving PHP code to be faster and/or more memory efficient)
• optimizing PHP execution (xcache can speed stuff up several times)
• caching of whole requests also does wonders, see mod_cache

Maybe, if your web isn't any CPU-intensive at all, and you need some extreme Req/S, try some different webserver (like nginx, or lighttpd) which behave better in such situations.