From 9e6051d194ac6292ac1cc7de2eaa78d665f36036 Mon Sep 17 00:00:00 2001 From: Richard Guo Date: Tue, 18 Jun 2024 16:25:19 +0900 Subject: [PATCH v6] 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. Author: Tender Wang Reviewed-by: Richard Guo, Alena Rybakina, Tomasz Rybak, Paul Jungwirth, Yuki Fujii Discussion: https://postgr.es/m/CAHewXNkPmtEXNfVQMou_7NqQmFABca9f4etjBtdbbm0ZKDmWvw@mail.gmail.com --- src/backend/optimizer/path/joinpath.c | 25 ++++++++++++++++ src/test/regress/expected/select_parallel.out | 30 +++++++++++++++++++ src/test/regress/sql/select_parallel.sql | 10 +++++++ 3 files changed, 65 insertions(+) diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c index 40eb58341c..02dd972492 100644 --- a/src/backend/optimizer/path/joinpath.c +++ b/src/backend/optimizer/path/joinpath.c @@ -2021,11 +2021,31 @@ 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); @@ -2082,6 +2102,11 @@ 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 c96285d1bb..7487ea0b82 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) + +-- the joinrel 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..9b019d31ed 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; + +-- the joinrel 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