PostgreSQL 9.3 beta: Federated databases and more

Threads are theoretically possible but have been held off primarily because it becomes very hard to reason about whether the code as it is is correct. There are a lot of shared structures (with other backends) with locking semantics based on individual processes and it's not immediately clear how that would interact with multiple threads.

That said, if you restrict yourself to just the executor you primarily have to deal with the memory allocator and the disk buffers. Is it possible to make that thread-safe? I'm not sure anyone has tried. I think with only a few weeks work you could probably make something functional. However, convincing everyone that the solution is as robust as the current setup is much much harder.