I’m working on a project involving the Radiant CMS and a legacy DB2 database. We need full-text search and initially I would have liked to use Sphinx (because Ferret is too unstable) but the available Rails plugins for Sphinx only work with MySql or Postgres. So I came across a little-known search engine called Xapian. It’s very fast, it’s used by Gmane to index millions of entries every day and (alas!) it works with every DB that Rails works with (which includes DB2).
So in order to use it with Radiant, I built a small extension that makes Radiant pages full-text-indexable. You can check it out on Github. It’s still very basic and has lots of room for improvement, but it’s a start.