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Commita8a968a

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Consider cheap startup paths in add_paths_to_append_rel
6b94e7a did this for ordered append paths to allow fast startupMergeAppends, however, nothing was done for the Append case.Here we adjust add_paths_to_append_rel() to have it build an AppendPathcontaining the cheapest startup paths from each of the child relationswhen the append rel has "consider_startup" set.Author: Andy Fan, David RowleyDiscussion:https://www.postgresql.org/message-id/CAKU4AWrXSkUV=Pt-gRxQT7EbfUeNssprGyNsB=5mJibFZ6S3ww@mail.gmail.com
1 parent0b053e7 commita8a968a

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‎src/backend/optimizer/path/allpaths.c

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@@ -1307,6 +1307,8 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
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{
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List*subpaths=NIL;
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boolsubpaths_valid= true;
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List*startup_subpaths=NIL;
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boolstartup_subpaths_valid= true;
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List*partial_subpaths=NIL;
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List*pa_partial_subpaths=NIL;
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List*pa_nonpartial_subpaths=NIL;
@@ -1346,6 +1348,20 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
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else
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subpaths_valid= false;
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/*
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* When the planner is considering cheap startup plans, we'll also
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* collect all the cheapest_startup_paths and build an AppendPath
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* containing those as subpaths.
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*/
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if (rel->consider_startup&&childrel->pathlist!=NIL&&
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childrel->cheapest_startup_path->param_info==NULL)
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accumulate_append_subpath(childrel->cheapest_startup_path,
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&startup_subpaths,
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NULL);
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else
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startup_subpaths_valid= false;
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/* Same idea, but for a partial plan. */
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if (childrel->partial_pathlist!=NIL)
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{
@@ -1478,6 +1494,11 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
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NIL,NULL,0, false,
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-1));
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/* build an AppendPath for the cheap startup paths, if valid */
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if (startup_subpaths_valid)
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add_path(rel, (Path*)create_append_path(root,rel,startup_subpaths,
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NIL,NIL,NULL,0, false,-1));
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/*
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* Consider an append of unordered, unparameterized partial paths. Make
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* it parallel-aware if possible.

‎src/test/regress/expected/union.out

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@@ -1432,3 +1432,24 @@ where (x = 0) or (q1 >= q2 and q1 <= q2);
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4567890123456789 | 4567890123456789 | 1
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(6 rows)
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--
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-- Test the planner's ability to produce cheap startup plans with Append nodes
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--
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-- Ensure we get a Nested Loop join between tenk1 and tenk2
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explain (costs off)
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select t1.unique1 from tenk1 t1
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inner join tenk2 t2 on t1.tenthous = t2.tenthous
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union all
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(values(1)) limit 1;
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QUERY PLAN
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--------------------------------------------------------
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Limit
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-> Append
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-> Nested Loop
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Join Filter: (t1.tenthous = t2.tenthous)
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-> Seq Scan on tenk1 t1
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-> Materialize
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-> Seq Scan on tenk2 t2
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-> Result
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(8 rows)
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‎src/test/regress/sql/union.sql

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@@ -540,3 +540,14 @@ select * from
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union all
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select*,1as xfrom int8_tbl b) ss
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where (x=0)or (q1>= q2and q1<= q2);
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--
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-- Test the planner's ability to produce cheap startup plans with Append nodes
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--
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-- Ensure we get a Nested Loop join between tenk1 and tenk2
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explain (costs off)
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selectt1.unique1from tenk1 t1
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inner join tenk2 t2ont1.tenthous=t2.tenthous
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union all
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(values(1))limit1;

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