Re: parallel joins, and better parallel explain

My idea is that you'd end up with a plan like this:

Gather
-> Hash Join
  -> Parallel Seq Scan
  -> Parallel Hash
    -> Parallel Seq Scan

Not only does this build only one copy of the hash table instead of N
copies, but we can parallelize the hash table construction itself by
having all workers insert in parallel, which is pretty cool. 

What I can confirm at this point is that
I've thought about the problem you're asking about here, and that
EnterpriseDB intends to contribute code to address it.