From 5abcae937f3b9e9cc5ea10721ce0d0a61f917e84 Mon Sep 17 00:00:00 2001 From: "Andrei V. Lepikhov" Date: Tue, 29 Apr 2025 12:54:59 +0200 Subject: [PATCH v0] Fix tuple_fraction calculation for merge append fractional path --- src/backend/optimizer/path/allpaths.c | 6 +++++- src/test/regress/expected/partition_join.out | 18 ++++++++++++++++++ src/test/regress/sql/partition_join.sql | 3 +++ 3 files changed, 26 insertions(+), 1 deletion(-) diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index 905250b3325..543550a9378 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -1891,7 +1891,11 @@ generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel, */ if (root->tuple_fraction > 0) { - double path_fraction = (1.0 / root->tuple_fraction); + double path_fraction = root->tuple_fraction; + + /* Convert absolute limit to a path fraction */ + if (path_fraction >= 1.) + path_fraction /= childrel->rows; cheapest_fractional = get_cheapest_fractional_path_for_pathkeys(childrel->pathlist, diff --git a/src/test/regress/expected/partition_join.out b/src/test/regress/expected/partition_join.out index 6101c8c7cf1..d5368186caa 100644 --- a/src/test/regress/expected/partition_join.out +++ b/src/test/regress/expected/partition_join.out @@ -5260,6 +5260,24 @@ SELECT x.id, y.id FROM fract_t x LEFT JOIN fract_t y USING (id) ORDER BY x.id DE Index Cond: (id = x_2.id) (11 rows) +EXPLAIN (COSTS OFF) -- Should use NestLoop with parameterised inner scan +SELECT x.id, y.id FROM fract_t x LEFT JOIN fract_t y USING (id) +ORDER BY x.id DESC LIMIT 2; + QUERY PLAN +-------------------------------------------------------------------------------- + Limit + -> Merge Append + Sort Key: x.id DESC + -> Nested Loop Left Join + -> Index Only Scan Backward using fract_t0_pkey on fract_t0 x_1 + -> Index Only Scan using fract_t0_pkey on fract_t0 y_1 + Index Cond: (id = x_1.id) + -> Nested Loop Left Join + -> Index Only Scan Backward using fract_t1_pkey on fract_t1 x_2 + -> Index Only Scan using fract_t1_pkey on fract_t1 y_2 + Index Cond: (id = x_2.id) +(11 rows) + -- -- Test Append's fractional paths -- diff --git a/src/test/regress/sql/partition_join.sql b/src/test/regress/sql/partition_join.sql index b76c5451001..30f15ee9acb 100644 --- a/src/test/regress/sql/partition_join.sql +++ b/src/test/regress/sql/partition_join.sql @@ -1224,6 +1224,9 @@ SELECT x.id, y.id FROM fract_t x LEFT JOIN fract_t y USING (id) ORDER BY x.id AS EXPLAIN (COSTS OFF) SELECT x.id, y.id FROM fract_t x LEFT JOIN fract_t y USING (id) ORDER BY x.id DESC LIMIT 10; +EXPLAIN (COSTS OFF) -- Should use NestLoop with parameterised inner scan +SELECT x.id, y.id FROM fract_t x LEFT JOIN fract_t y USING (id) +ORDER BY x.id DESC LIMIT 2; -- -- Test Append's fractional paths -- 2.39.5