postgres_fdw: Push down partition-wise aggregation.

Since commit 7012b132d07c2b4ea15b0b3cb1ea9f3278801d98, postgres_fdw
has been able to push down the toplevel aggregation operation to the
remote server.  Commit e2f1eb0ee30d144628ab523432320f174a2c8966 made
it possible to break down the toplevel aggregation into one
aggregate per partition.  This commit lets postgres_fdw push down
aggregation in that case just as it does at the top level.

In order to make this work, this commit adds an additional argument
to the GetForeignUpperPaths FDW API.  A matching argument is added
to the signature for create_upper_paths_hook.  Third-party code using
either of these will need to be updated.

Also adjust create_foreignscan_plan() so that it picks up the correct
set of relids in this case.

Jeevan Chalke, reviewed by Ashutosh Bapat and by me and with some
adjustments by me.  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
Discussion: http://postgr.es/m/CAM2+6=XPWujjmj5zUaBTGDoB38CemwcPmjkRy0qOcsQj_V+2sQ@mail.gmail.com

1 files changed, 18 insertions, 11 deletions

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index b387c6213b6..53ed6f8a17f 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -2206,12 +2206,13 @@ grouping_planner(PlannerInfo *root, bool inheritance_update,
 	if (final_rel->fdwroutine &&
 		final_rel->fdwroutine->GetForeignUpperPaths)
 		final_rel->fdwroutine->GetForeignUpperPaths(root, UPPERREL_FINAL,
-													current_rel, final_rel);
+													current_rel, final_rel,
+													NULL);
 
 	/* Let extensions possibly add some more paths */
 	if (create_upper_paths_hook)
 		(*create_upper_paths_hook) (root, UPPERREL_FINAL,
-									current_rel, final_rel);
+									current_rel, final_rel, NULL);
 
 	/* Note: currently, we leave it to callers to do set_cheapest() */
 }
@@ -4024,12 +4025,14 @@ create_ordinary_grouping_paths(PlannerInfo *root, RelOptInfo *input_rel,
 	if (grouped_rel->fdwroutine &&
 		grouped_rel->fdwroutine->GetForeignUpperPaths)
 		grouped_rel->fdwroutine->GetForeignUpperPaths(root, UPPERREL_GROUP_AGG,
-													  input_rel, grouped_rel);
+													  input_rel, grouped_rel,
+													  extra);
 
 	/* Let extensions possibly add some more paths */
 	if (create_upper_paths_hook)
 		(*create_upper_paths_hook) (root, UPPERREL_GROUP_AGG,
-									input_rel, grouped_rel);
+									input_rel, grouped_rel,
+									extra);
 }
 
 /*
@@ -4461,12 +4464,13 @@ create_window_paths(PlannerInfo *root,
 	if (window_rel->fdwroutine &&
 		window_rel->fdwroutine->GetForeignUpperPaths)
 		window_rel->fdwroutine->GetForeignUpperPaths(root, UPPERREL_WINDOW,
-													 input_rel, window_rel);
+													 input_rel, window_rel,
+													 NULL);
 
 	/* Let extensions possibly add some more paths */
 	if (create_upper_paths_hook)
 		(*create_upper_paths_hook) (root, UPPERREL_WINDOW,
-									input_rel, window_rel);
+									input_rel, window_rel, NULL);
 
 	/* Now choose the best path(s) */
 	set_cheapest(window_rel);
@@ -4765,12 +4769,13 @@ create_distinct_paths(PlannerInfo *root,
 	if (distinct_rel->fdwroutine &&
 		distinct_rel->fdwroutine->GetForeignUpperPaths)
 		distinct_rel->fdwroutine->GetForeignUpperPaths(root, UPPERREL_DISTINCT,
-													   input_rel, distinct_rel);
+													   input_rel, distinct_rel,
+													   NULL);
 
 	/* Let extensions possibly add some more paths */
 	if (create_upper_paths_hook)
 		(*create_upper_paths_hook) (root, UPPERREL_DISTINCT,
-									input_rel, distinct_rel);
+									input_rel, distinct_rel, NULL);
 
 	/* Now choose the best path(s) */
 	set_cheapest(distinct_rel);
@@ -4908,12 +4913,13 @@ create_ordered_paths(PlannerInfo *root,
 	if (ordered_rel->fdwroutine &&
 		ordered_rel->fdwroutine->GetForeignUpperPaths)
 		ordered_rel->fdwroutine->GetForeignUpperPaths(root, UPPERREL_ORDERED,
-													  input_rel, ordered_rel);
+													  input_rel, ordered_rel,
+													  NULL);
 
 	/* Let extensions possibly add some more paths */
 	if (create_upper_paths_hook)
 		(*create_upper_paths_hook) (root, UPPERREL_ORDERED,
-									input_rel, ordered_rel);
+									input_rel, ordered_rel, NULL);
 
 	/*
 	 * No need to bother with set_cheapest here; grouping_planner does not
@@ -6694,7 +6700,8 @@ create_partial_grouping_paths(PlannerInfo *root,
 
 		fdwroutine->GetForeignUpperPaths(root,
 										 UPPERREL_PARTIAL_GROUP_AGG,
-										 input_rel, partially_grouped_rel);
+										 input_rel, partially_grouped_rel,
+										 extra);
 	}
 
 	return partially_grouped_rel;