True. However, the reason Mnesia is better suited for in-RAM data sets is that its disk-only storage engine, dets, requires a potentially long repair process if the VM crashes and a dets table isn't closed properly. This could keep your table inaccessible for a while after you restart the VM.

Heh, the same principal restricting the mnesia database to 4 gigs on a 32 bit system is restricting the ram size to 4 gigs on a 32 bit system. (Some OS/Hardware magic can get around this but for the most systems this is true).