From 4ea6363d232ba3929fd7edd18e271217c85475ba Mon Sep 17 00:00:00 2001 From: Richard Guo Date: Tue, 18 Jun 2024 16:25:19 +0900 Subject: [PATCH v5] Consider materializing the cheapest inner path in parallel nestloop When generating non-parallel nestloop paths for each available outer path, we always consider materializing the cheapest inner path if feasible. Similarly, in this patch, we also consider materializing the cheapest inner path when building partial nestloop paths. This approach potentially reduces the need to rescan the inner side of a partial nestloop path for each outer tuple. --- src/backend/optimizer/path/joinpath.c | 26 ++++++++++++++++ src/test/regress/expected/select_parallel.out | 30 +++++++++++++++++++ src/test/regress/sql/select_parallel.sql | 10 +++++++ 3 files changed, 66 insertions(+) diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c index 5be8da9e09..11e1253bcd 100644 --- a/src/backend/optimizer/path/joinpath.c +++ b/src/backend/optimizer/path/joinpath.c @@ -2014,11 +2014,32 @@ consider_parallel_nestloop(PlannerInfo *root, JoinPathExtraData *extra) { JoinType save_jointype = jointype; + Path *inner_cheapest_total = innerrel->cheapest_total_path; + Path *matpath = NULL; ListCell *lc1; if (jointype == JOIN_UNIQUE_INNER) jointype = JOIN_INNER; + /* + * Consider materializing the cheapest inner path, unless: + * 1) we're doing JOIN_UNIQUE_INNER, because in this case we have to + * unique-ify the cheapest inner path, + * 2) enable_material is off, + * 3) the cheapest inner path is not parallel-safe, + * 4) the cheapest inner path is parameterized by the outer rel, or + * 5) the cheapest inner path materializes its output anyway. + */ + if (save_jointype != JOIN_UNIQUE_INNER && + enable_material && inner_cheapest_total->parallel_safe && + !PATH_PARAM_BY_REL(inner_cheapest_total, outerrel) && + !ExecMaterializesOutput(inner_cheapest_total->pathtype)) + { + matpath = (Path *) + create_material_path(innerrel, inner_cheapest_total); + Assert(matpath->parallel_safe); + } + foreach(lc1, outerrel->partial_pathlist) { Path *outerpath = (Path *) lfirst(lc1); @@ -2075,6 +2096,11 @@ consider_parallel_nestloop(PlannerInfo *root, try_partial_nestloop_path(root, joinrel, outerpath, mpath, pathkeys, jointype, extra); } + + /* Also consider materialized form of the cheapest inner path */ + if (matpath != NULL) + try_partial_nestloop_path(root, joinrel, outerpath, matpath, + pathkeys, jointype, extra); } } diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out index 87273fa635..d13f812f36 100644 --- a/src/test/regress/expected/select_parallel.out +++ b/src/test/regress/expected/select_parallel.out @@ -653,6 +653,36 @@ select count(*) from tenk1, tenk2 where tenk1.unique1 = tenk2.unique1; reset enable_hashjoin; reset enable_nestloop; +-- test parallel nestloop join path with materialization of the inner path. +alter table tenk2 set (parallel_workers = 0); +explain (costs off) + select * from tenk1 t1, tenk2 t2 where t1.two > t2.two; + QUERY PLAN +------------------------------------------- + Gather + Workers Planned: 4 + -> Nested Loop + Join Filter: (t1.two > t2.two) + -> Parallel Seq Scan on tenk1 t1 + -> Materialize + -> Seq Scan on tenk2 t2 +(7 rows) + +-- this is not parallel-safe due to the OFFSET clause in the subquery +explain (costs off) + select * from tenk1 t1, (select * from tenk2 t2 offset 0) t2 where t1.two > t2.two; + QUERY PLAN +------------------------------------------- + Nested Loop + Join Filter: (t1.two > t2.two) + -> Gather + Workers Planned: 4 + -> Parallel Seq Scan on tenk1 t1 + -> Materialize + -> Seq Scan on tenk2 t2 +(7 rows) + +alter table tenk2 reset (parallel_workers); -- test gather merge set enable_hashagg = false; explain (costs off) diff --git a/src/test/regress/sql/select_parallel.sql b/src/test/regress/sql/select_parallel.sql index 20376c03fa..67dac7f62b 100644 --- a/src/test/regress/sql/select_parallel.sql +++ b/src/test/regress/sql/select_parallel.sql @@ -266,6 +266,16 @@ select count(*) from tenk1, tenk2 where tenk1.unique1 = tenk2.unique1; reset enable_hashjoin; reset enable_nestloop; +-- test parallel nestloop join path with materialization of the inner path. +alter table tenk2 set (parallel_workers = 0); +explain (costs off) + select * from tenk1 t1, tenk2 t2 where t1.two > t2.two; + +-- this is not parallel-safe due to the OFFSET clause in the subquery +explain (costs off) + select * from tenk1 t1, (select * from tenk2 t2 offset 0) t2 where t1.two > t2.two; +alter table tenk2 reset (parallel_workers); + -- test gather merge set enable_hashagg = false; -- 2.43.0