On Sat, Oct 21, 2017 at 8:09 AM, Robert Haas <robertmh...@gmail.com> wrote: > On Tue, Oct 17, 2017 at 7:27 AM, Thomas Munro > <thomas.mu...@enterprisedb.com> wrote: >> While testing parallelism work I've wanted to be able to prevent >> gather nodes from running the plan in the leader process, and I've >> heard others say the same. One way would be to add a GUC >> "multiplex_gather", like in the attached patch. If you set it to off, >> Gather and Gather Merge won't run the subplan unless they have to >> because no workers could be launched. I thought about adding a new >> value for force_parallel_mode instead, but someone mentioned they >> might want to do this on a production system too and >> force_parallel_mode is not really for end users. Better ideas? > > I don't think overloading force_parallel_mode is a good idea, but > having some other GUC for this seems OK to me. Not sure I like > multiplex_gather, though.
How about parallel_leader_participation = on|off? The attached version has it that way, and adds regression tests to exercise on, off and off-but-couldn't-start-any-workers for both kinds of gather node. I'm not sure why node->need_to_rescan is initialised by both ExecGatherInit() and ExecGather(). Only the latter's value matters, right? I've added this to the January Commitfest. -- Thomas Munro http://www.enterprisedb.com
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