How much memory for 50 Users? How can I load test?

QUESTION: We have Drupal 4.7 with Civicrm 1.5. About 50 modules installed. How much Ram would be needed, assuming 50 users online at a time? We have a modest picture gallery.

RESPONSE 1: We just launched our Drupal + CiviCRM site — http://www.tik.be/ . It's now sending +8000 mails and there are currently 21 users and 115 guests online. On a dual core opteron with 1 GB RAM this doesn't cause any problems with memory. (and we also run a PHPBB and an OTRS ticketing system on the same server).

It DID cause problems with our mysql-server, he died because it ran out of connections. But I guess that can be fixed with some extra Drupal caching and tuning of mysql.

RESPONSE 2: You need to do some load testing with something like jmeter

Then on your server, log some memory snapshots from the /proc/ directory — and also from ps -aux

You can set up a cron job to do that.

Or there are some server monitoring apps like Munin you could install to take system snapshots.

It's a bit tricky to know which limits you are hitting, as chances are mysql and apache will swell to fill the available memory, so the thing to look for is whether the "swap" memory is being hit hard, which means the system is having to use virtual memory on the disk to meet the call from running apps.

You can also get a sense of how much memory Drupal is using using the Drupal developer module. BUT this will only show you how much mem PHP is using.

[Source. ]

There's some information at More Load Testing Stuff ...