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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
Download Patch File Download Diff File Expand all files Collapse all files

43
src/backend/optimizer/path/allpaths.c
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@ -95,7 +95,8 @@ static void set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
Index rti, RangeTblEntry *rte);
static void generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
List *live_childrels,
List *all_child_pathkeys);
List *all_child_pathkeys,
List *partitioned_rels);
static Path *get_cheapest_parameterized_child_path(PlannerInfo *root,
RelOptInfo *rel,
Relids required_outer);
@ -346,6 +347,14 @@ set_rel_size(PlannerInfo *root, RelOptInfo *rel,
/* Foreign table */
set_foreign_size(root, rel, rte);
}
else if (rte->relkind == RELKIND_PARTITIONED_TABLE)
{
/*
* A partitioned table without leaf partitions is marked
* as a dummy rel.
*/
set_dummy_rel_pathlist(rel);
}
else if (rte->tablesample != NULL)
{
/* Sampled relation */
@ -1259,6 +1268,16 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
List *all_child_pathkeys = NIL;
List *all_child_outers = NIL;
ListCell *l;
List *partitioned_rels = NIL;
RangeTblEntry *rte;
rte = planner_rt_fetch(rel->relid, root);
if (rte->relkind == RELKIND_PARTITIONED_TABLE)
{
partitioned_rels = get_partitioned_child_rels(root, rel->relid);
/* The root partitioned table is included as a child rel */
Assert(list_length(partitioned_rels) >= 1);
}
/*
* For every non-dummy child, remember the cheapest path. Also, identify
@ -1359,7 +1378,8 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
* if we have zero or one live subpath due to constraint exclusion.)
*/
if (subpaths_valid)
add_path(rel, (Path *) create_append_path(rel, subpaths, NULL, 0));
add_path(rel, (Path *) create_append_path(rel, subpaths, NULL, 0,
partitioned_rels));
/*
* Consider an append of partial unordered, unparameterized partial paths.
@ -1386,7 +1406,7 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
/* Generate a partial append path. */
appendpath = create_append_path(rel, partial_subpaths, NULL,
parallel_workers);
parallel_workers, partitioned_rels);
add_partial_path(rel, (Path *) appendpath);
}
@ -1396,7 +1416,8 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
*/
if (subpaths_valid)
generate_mergeappend_paths(root, rel, live_childrels,
all_child_pathkeys);
all_child_pathkeys,
partitioned_rels);
/*
* Build Append paths for each parameterization seen among the child rels.
@ -1438,7 +1459,8 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
if (subpaths_valid)
add_path(rel, (Path *)
create_append_path(rel, subpaths, required_outer, 0));
create_append_path(rel, subpaths, required_outer, 0,
partitioned_rels));
}
}
@ -1468,7 +1490,8 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
static void
generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
List *live_childrels,
List *all_child_pathkeys)
List *all_child_pathkeys,
List *partitioned_rels)
{
ListCell *lcp;
@ -1532,13 +1555,15 @@ generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
rel,
startup_subpaths,
pathkeys,
NULL));
NULL,
partitioned_rels));
if (startup_neq_total)
add_path(rel, (Path *) create_merge_append_path(root,
rel,
total_subpaths,
pathkeys,
NULL));
NULL,
partitioned_rels));
}
}
@ -1671,7 +1696,7 @@ set_dummy_rel_pathlist(RelOptInfo *rel)
rel->pathlist = NIL;
rel->partial_pathlist = NIL;
add_path(rel, (Path *) create_append_path(rel, NIL, NULL, 0));
add_path(rel, (Path *) create_append_path(rel, NIL, NULL, 0, NIL));
/*
* We set the cheapest path immediately, to ensure that IS_DUMMY_REL()