Really interesting. If I'm reading it right, every release (e.g. a homepage refresh) gets packaged up as a separate Lucene Solr Index. Interesting approach. One drawback is that they don't appear to keep previous indexes lying around, so it's not possible to see what your site looked like in the past (though there's always the Wayback Machine).<p>Having implemented a very similar system (albeit one that relies on SQL as a key-value version store, caching queries heavily and invalidating those caches where appropriate), very impressed with their implementation.