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Commit22d946b

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author
Richard Guo
committed
Consider materializing the cheapest inner path in parallel nestloop
When generating non-parallel nestloop paths for each available outerpath, we always consider materializing the cheapest inner path iffeasible. Similarly, in this patch, we also consider materializingthe cheapest inner path when building partial nestloop paths. Thisapproach potentially reduces the need to rescan the inner side of apartial nestloop path for each outer tuple.Author: Tender WangReviewed-by: Richard Guo, Robert Haas, David Rowley, Alena RybakinaReviewed-by: Tomasz Rybak, Paul Jungwirth, Yuki FujiiDiscussion:https://postgr.es/m/CAHewXNkPmtEXNfVQMou_7NqQmFABca9f4etjBtdbbm0ZKDmWvw@mail.gmail.com
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‎src/backend/optimizer/path/joinpath.c

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Original file line numberDiff line numberDiff line change
@@ -2021,11 +2021,31 @@ consider_parallel_nestloop(PlannerInfo *root,
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JoinPathExtraData*extra)
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{
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JoinTypesave_jointype=jointype;
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Path*inner_cheapest_total=innerrel->cheapest_total_path;
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Path*matpath=NULL;
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ListCell*lc1;
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if (jointype==JOIN_UNIQUE_INNER)
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jointype=JOIN_INNER;
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/*
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* Consider materializing the cheapest inner path, unless: 1) we're doing
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* JOIN_UNIQUE_INNER, because in this case we have to unique-ify the
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* cheapest inner path, 2) enable_material is off, 3) the cheapest inner
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* path is not parallel-safe, 4) the cheapest inner path is parameterized
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* by the outer rel, or 5) the cheapest inner path materializes its output
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* anyway.
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*/
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if (save_jointype!=JOIN_UNIQUE_INNER&&
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enable_material&&inner_cheapest_total->parallel_safe&&
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!PATH_PARAM_BY_REL(inner_cheapest_total,outerrel)&&
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!ExecMaterializesOutput(inner_cheapest_total->pathtype))
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{
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matpath= (Path*)
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create_material_path(innerrel,inner_cheapest_total);
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Assert(matpath->parallel_safe);
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}
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foreach(lc1,outerrel->partial_pathlist)
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{
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Path*outerpath= (Path*)lfirst(lc1);
@@ -2082,6 +2102,11 @@ consider_parallel_nestloop(PlannerInfo *root,
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try_partial_nestloop_path(root,joinrel,outerpath,mpath,
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pathkeys,jointype,extra);
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}
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/* Also consider materialized form of the cheapest inner path */
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if (matpath!=NULL)
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try_partial_nestloop_path(root,joinrel,outerpath,matpath,
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pathkeys,jointype,extra);
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}
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}
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‎src/test/regress/expected/select_parallel.out

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@@ -653,6 +653,36 @@ select count(*) from tenk1, tenk2 where tenk1.unique1 = tenk2.unique1;
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reset enable_hashjoin;
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reset enable_nestloop;
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-- test parallel nestloop join path with materialization of the inner path
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alter table tenk2 set (parallel_workers = 0);
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explain (costs off)
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select * from tenk1 t1, tenk2 t2 where t1.two > t2.two;
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QUERY PLAN
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-------------------------------------------
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Gather
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Workers Planned: 4
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-> Nested Loop
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Join Filter: (t1.two > t2.two)
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-> Parallel Seq Scan on tenk1 t1
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-> Materialize
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-> Seq Scan on tenk2 t2
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(7 rows)
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-- the joinrel is not parallel-safe due to the OFFSET clause in the subquery
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explain (costs off)
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select * from tenk1 t1, (select * from tenk2 t2 offset 0) t2 where t1.two > t2.two;
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QUERY PLAN
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-------------------------------------------
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Nested Loop
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Join Filter: (t1.two > t2.two)
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-> Gather
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Workers Planned: 4
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-> Parallel Seq Scan on tenk1 t1
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-> Materialize
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-> Seq Scan on tenk2 t2
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(7 rows)
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alter table tenk2 reset (parallel_workers);
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-- test gather merge
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set enable_hashagg = false;
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explain (costs off)

‎src/test/regress/sql/select_parallel.sql

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Original file line numberDiff line numberDiff line change
@@ -266,6 +266,16 @@ select count(*) from tenk1, tenk2 where tenk1.unique1 = tenk2.unique1;
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reset enable_hashjoin;
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reset enable_nestloop;
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-- test parallel nestloop join path with materialization of the inner path
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altertable tenk2set (parallel_workers=0);
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explain (costs off)
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select*from tenk1 t1, tenk2 t2wheret1.two>t2.two;
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-- the joinrel is not parallel-safe due to the OFFSET clause in the subquery
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explain (costs off)
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select*from tenk1 t1, (select*from tenk2 t2 offset0) t2wheret1.two>t2.two;
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altertable tenk2 reset (parallel_workers);
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-- test gather merge
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set enable_hashagg= false;
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