rails performance and msql driver

I'm sure this is documented all over the internet, except on the pages I happened to look at. I never knew until I was looking in my log for some other problem, and spotted this:

WARNING: You're using the Ruby-based MySQL library that ships with Rails.
This library is not suited for production. 
Please install the C-based MySQL library instead (gem install mysql).

At first I thought, what the hell, the ruby-based library "works on my machine", why bother? And I remembered how suckily my apps were performing. And "gem install mysql" - it couldn't really be easier, could it?

It couldn't except for a dependency on libmysqlclient15, to install which I first needed to update my ubuntu system (a 7.10 on Slicehost), and for the mysql gem I also needed to update rubygems itself. "gem install mysql" just refused to work until these two were done. My version of rubygems was hanging - apparently this happens if it hasn't been run in a while and needs to make a big refresh from the repository. Rubygems 1.2 doesn't have this problem, fortunately.

This was the full sequence:

sudo apt-get update
sudo apt-get install libmysqlclient15

wget http://rubyforge.org/frs/download.php/38646/rubygems-1.2.0.tgz
gunzip rubygems-1.2.0.tgz
tar xvf rubygems-1.2.0.tar
cd rubygems-1.2.0
sudo ruby ./setup.rb

sudo gem install mysql

mongrel_cluster_ctl restart

If you're thinking "what the hell, the ruby-based library works on my machine", change your thinking. This could transform your app from barely usable to pleasantly snappy.