> NoSQL doesn't replace SQL databases, it's looking to optimise a use case where transactions are not required. I'd be curious to know in what contexts anyone

> NoSQL doesn't replace SQL databases, it's looking to optimise a use case where transactions are not required. I'd be curious to know in what contexts anyone would not want transactions. I readily see the case for memcached or equivalent when it comes to caching -- it is very valid, and indeed useful, when slightly outdated data is perfectly acceptable. I can even picture how you might be using MongoDB to do the same, even if you admittedly have me wondering how you're invalidating the mess. For a persistent data store, however, I'm honestly at a loss. In my own experience, transactions are needed as soon as there's a remote possibility that a concurrent write may occur. Even embedded systems need them, when you're threading statements concurrently for performance reasons, or when you're subsequently merging local data with another node. (See CoreData/iCloud bugs for what occurs when you ignore ACID in the latter case.)