Mnesia supports ACID (Atomicity, Consistency, Isolation and Durability), but also offers the ability to perform in memory only operations on tables (at the expense of durability).

While Mnesia excels at scalability and low latency in transactions on horizontally fragmented data, one remaining challenge may be how it will scale in terms of very large datasets.

Although Armstrong says that Mnesia queries look a lot like SQL, he omits the fact that the similarity only becomes apparent after you've become quite good with Erlang.