Turning the database inside-out with Apache Samza
Immutability is hardly a cure-all, see the discussion here for why RethinkDB moved away from it: http://www.xaprb.com/blog/2013/12/28/immutability-mvcc-and-g...The reality is shared, mutable state is the most efficient way of working with memory-sized data. People can rant and rave all they want about the benefits of immutability vs mutability, but at the end of the day, if performance is important to you, you'd be best to ignore them.Actually, to be more honest, reality is more complicated still. MVCC that many databases use to get ACID semantics over a shared mutable dataset is really a combination of mutable and immutable.