On Thu, Jan 18, 2018 at 10:27 AM, Robert Haas <robertmh...@gmail.com> wrote: > On Thu, Jan 18, 2018 at 1:14 PM, Peter Geoghegan <p...@bowt.ie> wrote: >> That seems pretty far fetched. > > I don't think it is, and there are plenty of other examples. All you > need is a query plan that involves significant CPU work both below the > Gather node and above the Gather node. It's not difficult to find > plans like that; there are TPC-H queries that generate plans like > that.
You need to have a very selective qual in the worker, that eliminates most input (keeps the worker busy), and yet manages to keep the leader busy rather than waiting on input from the gather. >> But even if it wasn't, my position >> would not change. This could happen only because the planner >> determined that it was the cheapest plan when >> parallel_leader_participation happened to be off. But clearly a >> "degenerate parallel CREATE INDEX" will never be faster than a serial >> CREATE INDEX, and there is a simple way to always avoid one. So why >> not do so? > > That's an excellent argument for making parallel CREATE INDEX ignore > parallel_leader_participation entirely. I'm done making arguments about parallel_leader_participation. Tell me what you want, and I'll do it. -- Peter Geoghegan
