>I wonder what kind of numbers would we get by ditching JPA completely and using a non-relational DB like Redis
Yeah, I think we will most likely need to if we want to come close to the other implementations performance wise. Others use Memcache and I've seen MongoDB in use as well.
Perhaps I should just add performance tests for the rest of the SimplePush operations so that we have them covered and then look into using a non-relational DB. Once that is done we can revisit this performance task.
What do people thing about that?