[robotadam]

I'm a little confused by this; how do SQL databases not support more atomic operations that MongoDB, seeing as you have full control of the transactions themselves? Incrementing, adding to a list (generally done with inserting a row in another table), etc., are all standard operations.

[FooBarWidget]

Try upserting (update if exist, insert if not exist) a row, that doesn't work race-condition-free even in SERIALIZABLE isolation.