mysql

This morning, I was presented with quite the conundrum: one of my servers suddently started having about 4x the normal MySQL traffic it would have in a morning, and I had no indication as to why this was happening; traffic to the sites on the server was steady (no spikes), and I couldn't find any problems with any of the sites.

I've had to do this a couple times, and every time, I look around on Google for some good solutions, but don't find much. Basically, I have two tables of data, and I want to see if there are any rows in the first table that aren't in the second (or, conversely, I only want values that are in the first table AND the second).

To select rows in the first table that don't have any corresponding values in the second, try:

I've been getting errors like General error: Can't create/write to file, Error 2006: MySQL server has gone away, and other similar PDOExceptions and errors from time to time while developing on my Mac using MAMP Pro (this seems to happen more often with Drupal 7 sites than Drupal 6, for reasons I know not). I've noticed a few other developers are getting these errors too, and almost always on local environments as opposed to live servers.

Initially, when thinking about finally taking the plunge and purchasing a slice or two from Slicehost, I thought, "wow, this is going to be incredibly fast and awesome, compared to my Host Gator account!"

But, after setting everything up and putting Open Source Catholic live on the fresh slice, running free -m, and looking at the results, reality set in: 256 MB of RAM is not much to work with if you're running a Drupal site on a LAMP stack! Drupal usually consumes 15-40 MB of RAM per page view for a logged-in user, and if you have a site with 10 or so logged in users at any moment... well, bad things can happen.

For anonymous users, using Boost will help your site fly no matter the amount of RAM you have. But even so, a bunch of requests to uncached pages will cause your site to load a heck of a lot slower, and will fill up your RAM faster than a fire hose fills up an 8 oz. glass!

Using default Apache, MySQL and PHP settings, free -m showed a full 250 MB of RAM used, along with 400-500 swap space used (swap should be kept to a minimum—if you have a lot of swap usage, that means the hard drive is being used instead of RAM, and the hard drive is inherently many times slower!). After performing a few quick modifications to Apache and MySQL, I was able to get this number down to 140 MB RAM / 40-60 MB swap, on average.

I modified the server configuration in two different places: Apache's httpd.conf, and MySQL's my.cnf: