Hi, /* * GatherMergePath runs several copies of a plan in parallel and collects * the results, preserving their common sort order. For gather merge, the * parallel leader always executes the plan too, so we don't need single_copy. */ typedef struct GatherMergePath
The second sentence is not true as of commit e5253fdc, and the attached patch removes it. Even before that commit, the comment was a bit circular: the reason GatherMergePath doesn't need a single_copy field is because force_parallel_mode specifically means "try to stick a Gather node on top in a test mode with one worker and no leader participation", and this isn't a Gather node. Hmm. I wonder if we should rename force_parallel_mode to force_gather_node in v13. The current name has always seemed slightly misleading to me; it sounds like some kind of turbo boost button but really it's a developer-only test mode. Also, does it belong under DEVELOPER_OPTIONS instead of QUERY_TUNING_OTHER? I'm also wondering if the variable single_copy would be better named no_leader_participation or single_participant. I find "copy" a slightly strange way to refer to the number of copies *allowed to run*, but maybe that's just me. -- Thomas Munro https://enterprisedb.com
0001-Remove-misleading-comment-from-pathnodes.h.patch
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