I've been working with rails since 1.2 and I've never seen anyone actually do this. Every meaningful deployment I've seen uses postgres or mysql. (Or god forbid mongodb.) It takes very little time with yours sol statements
You can run rails on a single host using a database on the same server. I've done it and it works just fine as long as you tune things correctly.
I don't remember the exact details because it was a long time ago, but what I do remember is
- Limiting memory usage and number of connections for mysql
- Tracking maximum memory size of rails application servers so you didn't run out a memory by running too many of them
- Avoid writing unnecessarily memory intensive code (This is pretty easy in ruby if you know what you're doing)
- Avoiding using gems unless they were worth the memory use
- Configuring the frontend webserver to start dropping connections before it ran out of memory (I'm pretty sure that was just a guess)
- Using the frontend webserver to handle traffic whenever possible (mostly redirects)
- Using IP tables to block traffic before hitting the webserver
- Periodically checking memory use and turning off unnecessary services and cronjobs
I had the entire application running on a 512mb VPS with roughly 70mb to spare. It was a little less spare than I wanted but it worked.
Most of this was just rate limiting with extra steps. At the time rails couldn't use threads, so there was a hard limit on the number of concurrent tasks.
When the site went down it was due to rate limiting and not the server locking up. It was possible to ssh in and make firewall adjustments instead of a forced restart.
You can run rails on a single host using a database on the same server. I've done it and it works just fine as long as you tune things correctly.