On Sat, Jan 20, 2018 at 2:57 AM, Thomas Munro <thomas.mu...@enterprisedb.com> wrote: > On Sat, Jan 20, 2018 at 6:32 AM, Robert Haas <robertmh...@gmail.com> wrote: >> On Fri, Jan 19, 2018 at 12:16 PM, Peter Geoghegan <p...@bowt.ie> wrote: >>> Clarity on what I should do about parallel_leader_participation in the >>> next revision would be useful at this point. You seem to either want >>> me to remove it from consideration entirely, or to remove the code >>> that specifically disallows a "degenerate parallel CREATE INDEX". I >>> need a final answer on that. >> >> Right. I do think that we should do one of those things, and I lean >> towards removing it entirely, but I'm not entirely sure. Rather >> than making an executive decision immediately, I'd like to wait a few >> days to give others a chance to comment. I am hoping that we might get >> some other opinions, especially from Thomas who implemented >> parallel_leader_participation, or maybe Amit who has been reviewing >> recently, or anyone else who is paying attention to this thread. > > Well, I see parallel_leader_participation as having these reasons to exist: > > 1. Gather could in rare circumstances not run the plan in the leader. > This can hide bugs. It's good to be able to force that behaviour for > testing. >
Or reverse is also possible which means the workers won't get chance to run the plan in which case we can use parallel_leader_participation = off to test workers behavior. As said before, I see only that as the reason to keep parallel_leader_participation in this patch. If we decide to do that way, then I think we should remove the code that specifically disallows a "degenerate parallel CREATE INDEX" as that seems to be confusing. If we go this way, then I think we should use the wording suggested by Robert in one of its email [1] to describe the usage of parallel_leader_participation. BTW, is there any other way for "parallel create index" to force that the work is done by workers? I am insisting on having something which can test the code path in workers because we have found quite a few bugs using that idea. [1] - https://www.postgresql.org/message-id/CA%2BTgmoYN-YQU9JsGQcqFLovZ-C%2BXgp1_xhJQad%3DcunGG-_p5gg%40mail.gmail.com -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
