I've found Apache Solr the best approach to building a flexible, fast auto-complete service. Solr can spit results back in json so it's dead easy to write a sim

I've found Apache Solr the best approach to building a flexible, fast auto-complete service. Solr can spit results back in json so it's dead easy to write a simple API wrapper in whatever language you're using (go, python, ruby). You can then stick Varnish in front of the whole lot if the search space is relatively static and not ridiculously huge.