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Commit49525c4

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committed
Rewrite recurse_union_children to iterate, rather than recurse.
Also, rename it to plan_union_chidren, so the old name wasn'tvery descriptive. This results in a small net reduction in code,seems at least to me to be easier to understand, and savesspace on the process stack.Patch by me, reviewed and tested by Ashutosh Bapat and RajkumarRaghuwanshi.Discussion:http://postgr.es/m/CA+TgmoaLRAOqHmMZx=ESM3VDEPceg+-XXZsRXQ8GtFJO_zbMSw@mail.gmail.com
1 parent71cce90 commit49525c4

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1 file changed

+47
-53
lines changed

1 file changed

+47
-53
lines changed

‎src/backend/optimizer/prep/prepunion.c

Lines changed: 47 additions & 53 deletions
Original file line numberDiff line numberDiff line change
@@ -78,10 +78,10 @@ static Path *generate_nonunion_path(SetOperationStmt *op, PlannerInfo *root,
7878
List*refnames_tlist,
7979
List**pTargetList,
8080
double*pNumGroups);
81-
staticList*recurse_union_children(Node*setOp,PlannerInfo*root,
82-
SetOperationStmt*top_union,
83-
List*refnames_tlist,
84-
List**tlist_list);
81+
staticList*plan_union_children(PlannerInfo*root,
82+
SetOperationStmt*top_union,
83+
List*refnames_tlist,
84+
List**tlist_list);
8585
staticPath*make_union_unique(SetOperationStmt*op,Path*path,List*tlist,
8686
PlannerInfo*root);
8787
staticboolchoose_hashed_setop(PlannerInfo*root,List*groupClauses,
@@ -545,8 +545,6 @@ generate_union_path(SetOperationStmt *op, PlannerInfo *root,
545545
RelOptInfo*result_rel=fetch_upper_rel(root,UPPERREL_SETOP,NULL);
546546
doublesave_fraction=root->tuple_fraction;
547547
List*pathlist;
548-
List*child_tlists1;
549-
List*child_tlists2;
550548
List*tlist_list;
551549
List*tlist;
552550
Path*path;
@@ -571,13 +569,7 @@ generate_union_path(SetOperationStmt *op, PlannerInfo *root,
571569
* only one Append and unique-ification for the lot. Recurse to find such
572570
* nodes and compute their children's paths.
573571
*/
574-
pathlist=list_concat(recurse_union_children(op->larg,root,
575-
op,refnames_tlist,
576-
&child_tlists1),
577-
recurse_union_children(op->rarg,root,
578-
op,refnames_tlist,
579-
&child_tlists2));
580-
tlist_list=list_concat(child_tlists1,child_tlists2);
572+
pathlist=plan_union_children(root,op,refnames_tlist,&tlist_list);
581573

582574
/*
583575
* Generate tlist for Append plan node.
@@ -797,56 +789,58 @@ generate_nonunion_path(SetOperationStmt *op, PlannerInfo *root,
797789
* generate_union_path will force a fresh sort if the top level is a UNION.
798790
*/
799791
staticList*
800-
recurse_union_children(Node*setOp,PlannerInfo*root,
801-
SetOperationStmt*top_union,
802-
List*refnames_tlist,
803-
List**tlist_list)
792+
plan_union_children(PlannerInfo*root,
793+
SetOperationStmt*top_union,
794+
List*refnames_tlist,
795+
List**tlist_list)
804796
{
805-
List*result;
797+
List*pending_rels=list_make1(top_union);
798+
List*result=NIL;
806799
List*child_tlist;
807800

808-
if (IsA(setOp,SetOperationStmt))
801+
*tlist_list=NIL;
802+
803+
while (pending_rels!=NIL)
809804
{
810-
SetOperationStmt*op= (SetOperationStmt*)setOp;
805+
Node*setOp=linitial(pending_rels);
806+
807+
pending_rels=list_delete_first(pending_rels);
811808

812-
if (op->op==top_union->op&&
813-
(op->all==top_union->all||op->all)&&
814-
equal(op->colTypes,top_union->colTypes))
809+
if (IsA(setOp,SetOperationStmt))
815810
{
816-
/* Same UNION, so fold children into parent's subpath list */
817-
List*child_tlists1;
818-
List*child_tlists2;
811+
SetOperationStmt*op= (SetOperationStmt*)setOp;
819812

820-
result=list_concat(recurse_union_children(op->larg,root,
821-
top_union,
822-
refnames_tlist,
823-
&child_tlists1),
824-
recurse_union_children(op->rarg,root,
825-
top_union,
826-
refnames_tlist,
827-
&child_tlists2));
828-
*tlist_list=list_concat(child_tlists1,child_tlists2);
829-
returnresult;
813+
if (op->op==top_union->op&&
814+
(op->all==top_union->all||op->all)&&
815+
equal(op->colTypes,top_union->colTypes))
816+
{
817+
/* Same UNION, so fold children into parent */
818+
pending_rels=lcons(op->rarg,pending_rels);
819+
pending_rels=lcons(op->larg,pending_rels);
820+
continue;
821+
}
830822
}
823+
824+
/*
825+
* Not same, so plan this child separately.
826+
*
827+
* Note we disallow any resjunk columns in child results. This is
828+
* necessary since the Append node that implements the union won't do
829+
* any projection, and upper levels will get confused if some of our
830+
* output tuples have junk and some don't. This case only arises when
831+
* we have an EXCEPT or INTERSECT as child, else there won't be
832+
* resjunk anyway.
833+
*/
834+
result=lappend(result,recurse_set_operations(setOp,root,
835+
top_union->colTypes,
836+
top_union->colCollations,
837+
false,-1,
838+
refnames_tlist,
839+
&child_tlist,
840+
NULL));
841+
*tlist_list=lappend(*tlist_list,child_tlist);
831842
}
832843

833-
/*
834-
* Not same, so plan this child separately.
835-
*
836-
* Note we disallow any resjunk columns in child results. This is
837-
* necessary since the Append node that implements the union won't do any
838-
* projection, and upper levels will get confused if some of our output
839-
* tuples have junk and some don't. This case only arises when we have an
840-
* EXCEPT or INTERSECT as child, else there won't be resjunk anyway.
841-
*/
842-
result=list_make1(recurse_set_operations(setOp,root,
843-
top_union->colTypes,
844-
top_union->colCollations,
845-
false,-1,
846-
refnames_tlist,
847-
&child_tlist,
848-
NULL));
849-
*tlist_list=list_make1(child_tlist);
850844
returnresult;
851845
}
852846

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