"Datomic is not an update-in-place system. All data is retained by default." I'm becoming more and more convinced that your canonical data store should be appe

"Datomic is not an update-in-place system. All data is retained by default." I'm becoming more and more convinced that your canonical data store should be append-only whenever possible (see eg [1][2] for detailed arguments). It's nice to see first class support for this. [1] http://nathanmarz.com/blog/how-to-beat-the-cap-theorem.html http://nathanmarz.com/blog/how-to-beat-the-cap-theorem.html [2] http://martinfowler.com/articles/lmax.html http://martinfowler.com/articles/lmax.html EDIT: Just read through the whitepaper. Looks like the indexes / storage engine form an MVCC (http://en.wikipedia.org/wiki/Multiversion_concurrency_control http://en.wikipedia.org/wiki/Multiversion_concurrency_contro...) key-value store, similar to Clojure's STM. Peers cache data and run datalog queries locally. This could be either an available or consistent system, depending on how cache invalidation in peers works. In the available, eventually-consistent case you have the added benefit that all queries see a consistent snapshot of the system, even if that snapshot is not totally current. Like most of Hickey's work, the whole thing seems really obvious in hindsight. It also bears a lot of similarity to Nathan Marz' recommendations for data processing and schema design.