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Push target list evaluation through Gather Merge.

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We already do this for Gather, but it got overlooked for Gather Merge.

Amit Kapila, with review and minor revisions by Rushabh Lathia
and by me.

Discussion: http://postgr.es/m/CAA4eK1KUC5Uyu7qaifxrjpHxbSeoQh3yzwN3bThnJsmJcZ-qtA@mail.gmail.com
This commit is contained in:
Robert Haas
2017-11-13 16:33:56 -05:00
parent e64861c79b
commit 44ae64c388
4 changed files with 69 additions and 17 deletions
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3
src/backend/optimizer/plan/planner.c
View File

@ -5060,7 +5060,8 @@ create_ordered_paths(PlannerInfo *root,
path = (Path *)
create_gather_merge_path(root, ordered_rel,
path,
target, root->sort_pathkeys, NULL,
path->pathtarget,
root->sort_pathkeys, NULL,
&total_groups);
/* Add projection step if needed */

45
src/backend/optimizer/util/pathnode.c
View File

@ -2368,9 +2368,9 @@ create_projection_path(PlannerInfo *root,
* knows that the given path isn't referenced elsewhere and so can be modified
* in-place.
*
* If the input path is a GatherPath, we try to push the new target down to
* its input as well; this is a yet more invasive modification of the input
* path, which create_projection_path() can't do.
* If the input path is a GatherPath or GatherMergePath, we try to push the
* new target down to its input as well; this is a yet more invasive
* modification of the input path, which create_projection_path() can't do.
*
* Note that we mustn't change the source path's parent link; so when it is
* add_path'd to "rel" things will be a bit inconsistent. So far that has
@ -2407,31 +2407,44 @@ apply_projection_to_path(PlannerInfo *root,
(target->cost.per_tuple - oldcost.per_tuple) * path->rows;
/*
* If the path happens to be a Gather path, we'd like to arrange for the
* subpath to return the required target list so that workers can help
* project. But if there is something that is not parallel-safe in the
* target expressions, then we can't.
* If the path happens to be a Gather or GatherMerge path, we'd like to
* arrange for the subpath to return the required target list so that
* workers can help project. But if there is something that is not
* parallel-safe in the target expressions, then we can't.
*/
if (IsA(path, GatherPath) &&
if ((IsA(path, GatherPath) || IsA(path, GatherMergePath)) &&
is_parallel_safe(root, (Node *) target->exprs))
{
GatherPath *gpath = (GatherPath *) path;
/*
* We always use create_projection_path here, even if the subpath is
* projection-capable, so as to avoid modifying the subpath in place.
* It seems unlikely at present that there could be any other
* references to the subpath, but better safe than sorry.
*
* Note that we don't change the GatherPath's cost estimates; it might
* Note that we don't change the parallel path's cost estimates; it might
* be appropriate to do so, to reflect the fact that the bulk of the
* target evaluation will happen in workers.
*/
gpath->subpath = (Path *)
create_projection_path(root,
gpath->subpath->parent,
gpath->subpath,
target);
if (IsA(path, GatherPath))
{
GatherPath *gpath = (GatherPath *) path;
gpath->subpath = (Path *)
create_projection_path(root,
gpath->subpath->parent,
gpath->subpath,
target);
}
else
{
GatherMergePath *gmpath = (GatherMergePath *) path;
gmpath->subpath = (Path *)
create_projection_path(root,
gmpath->subpath->parent,
gmpath->subpath,
target);
}
}
else if (path->parallel_safe &&
!is_parallel_safe(root, (Node *) target->exprs))