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Add a new upper planner relation for partially-aggregated results.

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Up until now, we've abused grouped_rel->partial_pathlist as a place to
store partial paths that have been partially aggregate, but that's
really not correct, because a partial path for a relation is supposed
to be one which produces the correct results with the addition of only
a Gather or Gather Merge node, and these paths also require a Finalize
Aggregate step.  Instead, add a new partially_group_rel which can hold
either partial paths (which need to be gathered and then have
aggregation finalized) or non-partial paths (which only need to have
aggregation finalized).  This allows us to reuse generate_gather_paths
for partially_grouped_rel instead of writing new code, so that this
patch actually basically no net new code while making things cleaner,
simplifying things for pending patches for partition-wise aggregate.

Robert Haas and Jeevan Chalke.  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, Rafia Sabih, and me.

Discussion: http://postgr.es/m/CA+TgmobrzFYS3+U8a_BCy3-hOvh5UyJbC18rEcYehxhpw5=ETA@mail.gmail.com
Discussion: http://postgr.es/m/CA+TgmoZyQEjdBNuoG9-wC5GQ5GrO4544Myo13dVptvx+uLg9uQ@mail.gmail.com
This commit is contained in:
Robert Haas
2018-02-26 09:30:12 -05:00
parent 5b570d771b
commit 3bf05e096b
6 changed files with 154 additions and 153 deletions
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26
src/backend/optimizer/path/allpaths.c
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@ -488,7 +488,7 @@ set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
* we'll consider gathering partial paths for the parent appendrel.)
*/
if (rel->reloptkind == RELOPT_BASEREL)
generate_gather_paths(root, rel);
generate_gather_paths(root, rel, false);
/*
* Allow a plugin to editorialize on the set of Paths for this base
@ -2444,27 +2444,42 @@ set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
* This must not be called until after we're done creating all partial paths
* for the specified relation. (Otherwise, add_partial_path might delete a
* path that some GatherPath or GatherMergePath has a reference to.)
*
* If we're generating paths for a scan or join relation, override_rows will
* be false, and we'll just use the relation's size estimate. When we're
* being called for a partially-grouped path, though, we need to override
* the rowcount estimate. (It's not clear that the particular value we're
* using here is actually best, but the underlying rel has no estimate so
* we must do something.)
*/
void
generate_gather_paths(PlannerInfo *root, RelOptInfo *rel)
generate_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows)
{
Path *cheapest_partial_path;
Path *simple_gather_path;
ListCell *lc;
double rows;
double *rowsp = NULL;
/* If there are no partial paths, there's nothing to do here. */
if (rel->partial_pathlist == NIL)
return;
/* Should we override the rel's rowcount estimate? */
if (override_rows)
rowsp = &rows;
/*
* The output of Gather is always unsorted, so there's only one partial
* path of interest: the cheapest one. That will be the one at the front
* of partial_pathlist because of the way add_partial_path works.
*/
cheapest_partial_path = linitial(rel->partial_pathlist);
rows =
cheapest_partial_path->rows * cheapest_partial_path->parallel_workers;
simple_gather_path = (Path *)
create_gather_path(root, rel, cheapest_partial_path, rel->reltarget,
NULL, NULL);
NULL, rowsp);
add_path(rel, simple_gather_path);
/*
@ -2479,8 +2494,9 @@ generate_gather_paths(PlannerInfo *root, RelOptInfo *rel)
if (subpath->pathkeys == NIL)
continue;
rows = subpath->rows * subpath->parallel_workers;
path = create_gather_merge_path(root, rel, subpath, rel->reltarget,
subpath->pathkeys, NULL, NULL);
subpath->pathkeys, NULL, rowsp);
add_path(rel, &path->path);
}
}
@ -2653,7 +2669,7 @@ standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
generate_partitionwise_join_paths(root, rel);
/* Create GatherPaths for any useful partial paths for rel */
generate_gather_paths(root, rel);
generate_gather_paths(root, rel, false);
/* Find and save the cheapest paths for this rel */
set_cheapest(rel);