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Don't scan partitioned tables.

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Partitioned tables do not contain any data; only their unpartitioned
descendents need to be scanned.  However, the partitioned tables still
need to be locked, even though they're not scanned.  To make that
work, Append and MergeAppend relations now need to carry a list of
(unscanned) partitioned relations that must be locked, and InitPlan
must lock all partitioned result relations.

Aside from the obvious advantage of avoiding some work at execution
time, this has two other advantages.  First, it may improve the
planner's decision-making in some cases since the empty relation
might throw things off.  Second, it paves the way to getting rid of
the storage for partitioned tables altogether.

Amit Langote, reviewed by me.

Discussion: http://postgr.es/m/6837c359-45c4-8044-34d1-736756335a15@lab.ntt.co.jp
This commit is contained in:
Robert Haas
2017-03-21 09:48:04 -04:00
parent d5286aa905
commit d3cc37f1d8
27 changed files with 537 additions and 164 deletions
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10
src/backend/optimizer/util/pathnode.c
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@ -1201,7 +1201,7 @@ create_tidscan_path(PlannerInfo *root, RelOptInfo *rel, List *tidquals,
*/
AppendPath *
create_append_path(RelOptInfo *rel, List *subpaths, Relids required_outer,
int parallel_workers)
int parallel_workers, List *partitioned_rels)
{
AppendPath *pathnode = makeNode(AppendPath);
ListCell *l;
@ -1216,6 +1216,7 @@ create_append_path(RelOptInfo *rel, List *subpaths, Relids required_outer,
pathnode->path.parallel_workers = parallel_workers;
pathnode->path.pathkeys = NIL; /* result is always considered
* unsorted */
pathnode->partitioned_rels = partitioned_rels;
pathnode->subpaths = subpaths;
/*
@ -1258,7 +1259,8 @@ create_merge_append_path(PlannerInfo *root,
RelOptInfo *rel,
List *subpaths,
List *pathkeys,
Relids required_outer)
Relids required_outer,
List *partitioned_rels)
{
MergeAppendPath *pathnode = makeNode(MergeAppendPath);
Cost input_startup_cost;
@ -1274,6 +1276,7 @@ create_merge_append_path(PlannerInfo *root,
pathnode->path.parallel_safe = rel->consider_parallel;
pathnode->path.parallel_workers = 0;
pathnode->path.pathkeys = pathkeys;
pathnode->partitioned_rels = partitioned_rels;
pathnode->subpaths = subpaths;
/*
@ -3105,7 +3108,7 @@ create_lockrows_path(PlannerInfo *root, RelOptInfo *rel,
ModifyTablePath *
create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
CmdType operation, bool canSetTag,
Index nominalRelation,
Index nominalRelation, List *partitioned_rels,
List *resultRelations, List *subpaths,
List *subroots,
List *withCheckOptionLists, List *returningLists,
@ -3172,6 +3175,7 @@ create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
pathnode->operation = operation;
pathnode->canSetTag = canSetTag;
pathnode->nominalRelation = nominalRelation;
pathnode->partitioned_rels = partitioned_rels;
pathnode->resultRelations = resultRelations;
pathnode->subpaths = subpaths;
pathnode->subroots = subroots;