Here are a couple of issues and/or fixes if you are running a Rails/Mysql application on a 256MB server - specifically I am (was) running a web site built using Radiant (a Rails/Mysql based CMS) on a 256MB slice at Slicehost.
The site is effectively static but this weekend Slicehost sent me an automated email telling me the slice was swapping heavily. Turns out that the default settings for Mysqld use the InnoDB engine and that chews up a lot of memory - well over 150MB.
Two solutions - turn off InnoDB or upgrade to a slice with more memory (for just under twice the cost).
To turn off InnoDB go into /etc/mysql/my.cnf, uncomment the line 'skip-innodb' and restart. That should drop your memory use by around 100MB.
But the settings for my existing Radiant app (running with Rails 2.3.2) appear to require InnoDB and Phusion Passenger fails to start the app with that setting.
Rather than mess with an app that has been fine, I decided to upgrade to a large slice. I dumped the database contents as a precaution but then just followed the resize steps from the Slicehost slice management page. Worked like a charm - everything came back up and works fine. Running 'free -m' or 'top' shows I've got memory to spare for now. It's costing me $38/month instead of $20, but I can stay with a default configuration for my database, etc. and that is worth quite a bit in itself.
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