I have a dedicated server that has 12GB of RAM and Dual Nahalem Quad Core processors. My site usually only has about 50-100 users online at a time (though once I get the server optimized I plan on advertising and estimate the number to be closer to 250, which should still be very easily handled by this server). For some reason, even with these low numbers, the site seems to lag quite often with almost no server load.
I have been using mysqltuner.pl to try to get some things setup better in my.cnf. At this user level the site runs about 200 queries per second and is about 50/50 reads/writes.When it comes to Apache settings, I would have absolutely no idea what to change.
I am mainly just looking for general suggestions of things to update to better optimize performance of the server so that pages actually load quickly. It is worth noting that the pages loaded fairly quickly until a few days ago when the average online increased by 3-4x (though the server load hasn't really increased).
This is a CentOS 5.4 server if that matters.