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Implement partition-wise grouping/aggregation.

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If the partition keys of input relation are part of the GROUP BY
clause, all the rows belonging to a given group come from a single
partition.  This allows aggregation/grouping over a partitioned
relation to be broken down * into aggregation/grouping on each
partition.  This should be no worse, and often better, than the normal
approach.

If the GROUP BY clause does not contain all the partition keys, we can
still perform partial aggregation for each partition and then finalize
aggregation after appending the partial results.  This is less certain
to be a win, but it's still useful.

Jeevan Chalke, Ashutosh Bapat, Robert Haas.  The larger patch series
of which this patch is a part was also reviewed and tested by Antonin
Houska, Rajkumar Raghuwanshi, David Rowley, Dilip Kumar, Konstantin
Knizhnik, Pascal Legrand, and Rafia Sabih.

Discussion: http://postgr.es/m/CAM2+6=V64_xhstVHie0Rz=KPEQnLJMZt_e314P0jaT_oJ9MR8A@mail.gmail.com
This commit is contained in:
Robert Haas
2018-03-22 12:49:48 -04:00
parent 2058d6a22b
commit e2f1eb0ee3
17 changed files with 2552 additions and 214 deletions
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17
src/backend/optimizer/path/allpaths.c
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@ -134,8 +134,6 @@ static void subquery_push_qual(Query *subquery,
static void recurse_push_qual(Node *setOp, Query *topquery,
RangeTblEntry *rte, Index rti, Node *qual);
static void remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel);
static void add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
List *live_childrels);
/*
@ -1326,7 +1324,7 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
* parameterization or ordering. Similarly it collects partial paths from
* non-dummy children to create partial append paths.
*/
static void
void
add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
List *live_childrels)
{
@ -1413,8 +1411,12 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
* If child has an unparameterized cheapest-total path, add that to
* the unparameterized Append path we are constructing for the parent.
* If not, there's no workable unparameterized path.
*
* With partitionwise aggregates, the child rel's pathlist may be
* empty, so don't assume that a path exists here.
*/
if (childrel->cheapest_total_path->param_info == NULL)
if (childrel->pathlist != NIL &&
childrel->cheapest_total_path->param_info == NULL)
accumulate_append_subpath(childrel->cheapest_total_path,
&subpaths, NULL);
else
@ -1682,6 +1684,13 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
Path *subpath;
if (childrel->pathlist == NIL)
{
/* failed to make a suitable path for this child */
subpaths_valid = false;
break;
}
subpath = get_cheapest_parameterized_child_path(root,
childrel,
required_outer);