Hardware and performance

Hi,
You might want to go in for a bit of memory performance tuning; I'm no expert but here are my thoughts:

• Apache is suffering process bloat (common with php and other dynamic content), and the memory each thread consumes will not automatically be freed: consider lowering MaxRequestsPerChild in httpd.conf to as low as 20-30 (if you set it any lower the overhead of forking begins to outweigh the benefits). Also check the memory_limit in php.ini, reduce it to at least 16M.
• Once you've done this, check the process table again to see how much memory is consumed by each apache instance on average (should be much lower). As a rule of thumb, if you divide your total available ram (i.e. free memory when apache is not running) by this amount it will give you a value for MaxClients, and you can guesstimate StartServers, MinSpareServers, and MaxSpareServers similarly.
• The other big memory hogger is mysql, and you should try tweaking the memory usage there as well (see http://dev.mysql.com/doc/refman/5.0/en/server-parameters.html).

There are more general factors to do with how your system is setup: What else is the server doing that could consume memory? Depending on your memory/processor balance should you recompile apache with preforking? Does your distro (e.g. Fedora) preload bloat? Tuning LAMP is a science in itself, and if you have the patience you can sometimes gain far greater performance improvements than just throwing more hardware at the problem. Having said that, in your case a bit more RAM wouldn't go amiss

As an example, our setup is a reasonably beefy dual xeon with raid1, dual NICs and 2G of RAM, running Gentoo:

In httpd.conf:
MaxKeepAliveRequests 150
KeepAliveTimeout 5 #occasional 56k user
<ifmodule>
    StartServers         8
    MinSpareServers      8
    MaxSpareServers     15
    MaxClients         250
    MaxRequestsPerChild 30
</ifmodule>

In my.cnf:

key_buffer 			= 32M
max_allowed_packet 		= 1M
table_cache 			= 192 #Moodle uses a lot of tables
sort_buffer_size 		= 2M
net_buffer_length 		= 8K
read_buffer_size 		= 512K
read_rnd_buffer_size 		= 512K
myisam_sort_buffer_size 	= 8M

Server stats page is here.

You could check the moodle documentation page, but you'll find more information on the more general topic of LAMP performance tuning by googling.