From 963cb6ed7d27cd7112c4fc4b4fb138b63edf087e Mon Sep 17 00:00:00 2001 From: James Coleman Date: Mon, 6 Apr 2020 20:45:57 -0400 Subject: [PATCH v1 2/2] Comment show_incremental_sort_info assumtions It's not immediately obvious when reading this code that ignoring the prefix group info is correct if there are no full groups, so add a comment explaining the rationale. --- src/backend/commands/explain.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c index b1a20eba27..b8fd542c9b 100644 --- a/src/backend/commands/explain.c +++ b/src/backend/commands/explain.c @@ -2884,6 +2884,15 @@ show_incremental_sort_info(IncrementalSortState *incrsortstate, if (!es->analyze) return; + /* + * Since we never have any prefix groups unless we've first sorted a full + * groups and transitioned modes (copying the tuples into a prefix group), + * we don't need to do anything if there were 0 full groups. + * + * We still have to continue after this block if there are no full groups, + * though, since it's possible that we have workers that did real work even + * if the leader didn't participate. + */ if (fullsortGroupInfo->groupCount > 0) { show_incremental_sort_group_info(fullsortGroupInfo, "Full-sort", true, es); @@ -2915,6 +2924,13 @@ show_incremental_sort_info(IncrementalSortState *incrsortstate, */ fullsortGroupInfo = &incsort_info->fullsortGroupInfo; prefixsortGroupInfo = &incsort_info->prefixsortGroupInfo; + + /* + * Since we never have any prefix groups unless we've first sorted + * a full groups and transitioned modes (copying the tuples into a + * prefix group), we don't need to do anything if there were 0 full + * groups. + */ if (fullsortGroupInfo->groupCount == 0 && prefixsortGroupInfo->groupCount == 0) continue; -- 2.17.1