Should be quite easy to do equijoins especially if you're joining a couple thousand rows at most at a time; it only gets hairier when you're joining all records of very large tables that don't necessarily fit in memory, which is not very OLTP-y.

With regards to persistence, I'm really curious to hear how you're planning to have durability without writing something to disk on every transaction. It could work if you're relaxing the definition of durable to mean written to memory on at least $n$ nodes, though that's likely to be surprising to someone with a stricter definition of durable.

Edit: By the way, it's really cool that you have a C++ implementation of actors, I'll have to look into it. Have you thought about turning that into a library?