diff options
Diffstat (limited to 'src/backend')
| -rw-r--r-- | src/backend/optimizer/plan/planner.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c index d6ba7589f3a..000d757bdd8 100644 --- a/src/backend/optimizer/plan/planner.c +++ b/src/backend/optimizer/plan/planner.c @@ -5672,6 +5672,14 @@ select_active_windows(PlannerInfo *root, WindowFuncLists *wflists) * Sort the windows by the required sorting clauses. First, compare the sort * clauses themselves. Second, if one window's clauses are a prefix of another * one's clauses, put the window with more sort clauses first. + * + * We purposefully sort by the highest tleSortGroupRef first. Since + * tleSortGroupRefs are assigned for the query's DISTINCT and ORDER BY first + * and because here we sort the lowest tleSortGroupRefs last, if a + * WindowClause is sharing a tleSortGroupRef with the query's DISTINCT or + * ORDER BY clause, this makes it more likely that the final WindowAgg will + * provide presorted input for the query's DISTINCT or ORDER BY clause, thus + * reducing the total number of sorts required for the query. */ static int common_prefix_cmp(const void *a, const void *b) |