Active Record problem, MySQL overloaded? Server out of memory?

[eluser]meridimus[/eluser]
Error in db_active_rec on line 1080

Hi, I run the site Johnny Two Shoes (http://www.johnnytwoshoes.com/) and I get quite a lot of traffic. Over 1 million page views a month, around 300k unique visitors a month.

I am using CI 1.7.2 (whatever the latest one was before it went to 2.0) and I have a problem (it's been happening for a long time, on multiple servers) where basically, every now and again (at the moment it happens almost daily) the database server crashes and CI db_active_rec class responds that num_rows() on line 1080 doesn't work (Fatal Error).

I have googled this and searched this forum to no avail, is anyone else running CI on a site as big as mine? How did you deal with the problems like this?

More about my servers:

I am running on the MediaTemple Grid Service (gs) with a separate db server on their (ve) service, basically a minimum linux installation of which I put the latest stable version of MySQL. I moved from running everything on the (gs) to the (ve) because of this problem and doing this would give me more memory to run my database queries on as things got more and more complicated.

I wrote all the code for the site myself, didn't use any off the shelf forum package or anything, but I am in love with CI and would like to get it working much better.

I'm sure it's a problem with my setup, I think CI is just throwing an error because MySQL is screwed up, but I need help getting this right. Is there anyone I can employ/help me to look into this? Someone you guys trust from the forums? My knowledge becomes limited when a site becomes this large and I can't begin to put aside a large amount of time to fix it.

What should I do? I want to continue using CI, I love it and I love MediaTemple as a host, I think the problem lies with my MySQL configuration. Anything I should check?

I'm running Ubuntu 9.10, MySQL version: 5.1.37-1ubuntu5.4

Thanks for any help.