From 74b98007437540bb3fd4b91725835eee330b7703 Mon Sep 17 00:00:00 2001 From: Evdokimov Ilia Date: Mon, 7 Sep 2026 20:33:06 +0300 Subject: [PATCH v2] Use exact join size estimate for plain inner merge/hash joins For a plain inner join, path->jpath.path.rows already equals the number of tuples passing the merge/hash clauses, so final_cost_mergejoin()/final_cost_hashjoin() can use it directly instead of recomputing an approximation via approx_tuple_count(). For SEMI/LEFT/FULL joins this doesn't hold, so keep the substitution JOIN_INNER-only. --- src/backend/optimizer/path/costsize.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c index 7bbddb8bee4..d9714369374 100644 --- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -4058,7 +4058,11 @@ final_cost_mergejoin(PlannerInfo *root, MergePath *path, * Get approx # tuples passing the mergequals. We use approx_tuple_count * here because we need an estimate done with JOIN_INNER semantics. */ - mergejointuples = approx_tuple_count(root, &path->jpath, mergeclauses); + if (path->jpath.jointype == JOIN_INNER && + list_length(path->jpath.joinrestrictinfo) == list_length(mergeclauses)) + mergejointuples = path->jpath.path.rows; + else + mergejointuples = approx_tuple_count(root, &path->jpath, mergeclauses); /* * When there are equal merge keys in the outer relation, the mergejoin @@ -4711,6 +4715,8 @@ final_cost_hashjoin(PlannerInfo *root, HashPath *path, hashjointuples = outer_path_rows - outer_matched_rows; else if (path->jpath.jointype == JOIN_SEMI || extra->inner_unique) hashjointuples = outer_matched_rows; + else if (path->jpath.jointype == JOIN_INNER && list_length(path->jpath.joinrestrictinfo) == list_length(hashclauses)) + hashjointuples = path->jpath.path.rows; else hashjointuples = approx_tuple_count(root, &path->jpath, hashclauses); -- 2.34.1