I have just completed the move from one type of NoSQL database (couchdb) to another (mongodb). The speed increase is exhilarating, though I don't know by how much. The comparisons are not cached, they are computed on the fly: and the speed is the fruit of good design and careful implementation. As I said all along, conventional approaches based on XML are just too inefficient and inadequate. This design, based on multi-version documents, and hosted on a Jetty/Java service with a C core, is faster than any other such service I know of, and it is more flexible. There is also the new C-version of nmerge yet to add, which should increase capacity and speed further. Try out the test interface for yourself.