v2_optimize_row_numbers_frameoptions_when_possible.patch

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 5d0fd6e072..74a8bafd8b 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -38,6 +38,7 @@
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
+#include "nodes/supportnodes.h"
 #ifdef OPTIMIZER_DEBUG
 #include "nodes/print.h"
 #endif
@@ -207,6 +208,8 @@ static PathTarget *make_partial_grouping_target(PlannerInfo *root,
 												PathTarget *grouping_target,
 												Node *havingQual);
 static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist);
+static void optimize_window_clauses(PlannerInfo *root,
+									WindowFuncLists *wflists);
 static List *select_active_windows(PlannerInfo *root, WindowFuncLists *wflists);
 static PathTarget *make_window_input_target(PlannerInfo *root,
 											PathTarget *final_target,
@@ -1422,7 +1425,16 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 			wflists = find_window_functions((Node *) root->processed_tlist,
 											list_length(parse->windowClause));
 			if (wflists->numWindowFuncs > 0)
+			{
+				/*
+				 * See if any modifications can be made to each WindowClause
+				 * to allow the executor to execute the WindowFuncs more
+				 * quickly.
+				 */
+				optimize_window_clauses(root, wflists);
+
 				activeWindows = select_active_windows(root, wflists);
+			}
 			else
 				parse->hasWindowFuncs = false;
 		}
@@ -5391,6 +5403,85 @@ postprocess_setop_tlist(List *new_tlist, List *orig_tlist)
 	return new_tlist;
 }
 
+/*
+ * optimize_window_clauses
+ *		Call each WindowFunc's prosupport function to see if we're able to
+ *		make any adjustments to any of the WindowClause's so that the executor
+ *		can execute the window functions in a more optimal way.
+ *
+ * Currently we only allow adjustments to the WindowClause's frameOptions.  We
+ * may allow more things to be done here in the future.
+ */
+static void
+optimize_window_clauses(PlannerInfo *root, WindowFuncLists *wflists)
+{
+	List	   *windowClause = root->parse->windowClause;
+	ListCell *lc;
+
+	foreach(lc, windowClause)
+	{
+		WindowClause *wc = lfirst_node(WindowClause, lc);
+		ListCell *lc2;
+		int		optimizedFrameOptions = 0;
+
+		Assert(wc->winref <= wflists->maxWinRef);
+
+		/* skip any WindowClauses that have no WindowFuncs */
+		if (wflists->windowFuncs[wc->winref] == NIL)
+			continue;
+
+		foreach(lc2, wflists->windowFuncs[wc->winref])
+		{
+			SupportRequestOptimizeWindowClause req;
+			SupportRequestOptimizeWindowClause *res;
+			WindowFunc *wfunc = lfirst_node(WindowFunc, lc2);
+			Oid		prosupport;
+
+			prosupport = get_func_support(wfunc->winfnoid);
+
+			/* Check if there's a support function for 'wfunc' */
+			if (!OidIsValid(prosupport))
+				break;		/* can't optimize this WindowClause */
+
+			req.type = T_SupportRequestOptimizeWindowClause;
+			req.window_clause = wc;
+			req.window_func = wfunc;
+			req.frameOptions = wc->frameOptions;
+
+			/* call the support function */
+			res = (SupportRequestOptimizeWindowClause *)
+				DatumGetPointer(OidFunctionCall1(prosupport,
+					PointerGetDatum(&req)));
+
+			/*
+			 * Skip to next WindowClause if the support function does not
+			 * support this request type.
+			 */
+			if (res == NULL)
+				break;
+
+			/*
+			 * Save these frameOptions for the first WindowFunc for this
+			 * WindowClause.
+			 */
+			if (foreach_current_index(lc2) == 0)
+				optimizedFrameOptions = res->frameOptions;
+
+			/*
+			 * On subsequent WindowFuncs, if the frameOptions are not the same
+			 * then we're unable to optimize the frameOptions for this
+			 * WindowClause.
+			 */
+			else if (optimizedFrameOptions != res->frameOptions)
+				break;			/* skip to the next WindowClause, if any */
+		}
+
+		/* adjust the frameOptions if all WindowFunc's agree that it's ok */
+		if (lc2 == NULL)
+			wc->frameOptions = optimizedFrameOptions;
+	}
+}
+
 /*
  * select_active_windows
  *		Create a list of the "active" window clauses (ie, those referenced
diff --git a/src/backend/utils/adt/windowfuncs.c b/src/backend/utils/adt/windowfuncs.c
index 596564fa15..3bf90813cf 100644
--- a/src/backend/utils/adt/windowfuncs.c
+++ b/src/backend/utils/adt/windowfuncs.c
@@ -107,6 +107,23 @@ window_row_number_support(PG_FUNCTION_ARGS)
 		PG_RETURN_POINTER(req);
 	}
 
+	if (IsA(rawreq, SupportRequestOptimizeWindowClause))
+	{
+		SupportRequestOptimizeWindowClause *req = (SupportRequestOptimizeWindowClause *) rawreq;
+
+		/*
+		 * The frame options can always become "ROWS BETWEEN UNBOUNDED
+		 * PRECEDING AND CURRENT ROW".  row_number() always just increments
+		 * by 1 with each row in the partition.  Using ROWS instead of RANGE
+		 * saves effort during execution.
+		 */
+		req->frameOptions = (FRAMEOPTION_ROWS |
+							 FRAMEOPTION_START_UNBOUNDED_PRECEDING |
+							 FRAMEOPTION_END_CURRENT_ROW);
+
+		PG_RETURN_POINTER(req);
+	}
+
 	PG_RETURN_POINTER(NULL);
 }
 
@@ -149,6 +166,26 @@ window_rank_support(PG_FUNCTION_ARGS)
 		PG_RETURN_POINTER(req);
 	}
 
+	if (IsA(rawreq, SupportRequestOptimizeWindowClause))
+	{
+		SupportRequestOptimizeWindowClause *req = (SupportRequestOptimizeWindowClause *) rawreq;
+
+		/*
+		 * rank() is coded in such a way that it returns "(COUNT (*) OVER
+		 *(<opt> RANGE UNBOUNDED PRECEDING) - COUNT (*) OVER (<opt> RANGE
+		 * CURRENT ROW) + 1 )" regardless of the frame options.  We'll set the
+		 * frame options to "ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW"
+		 * so they agree with what window_row_number_support() optimized the
+		 * frame options to be.  Using ROWS instead of RANGE saves effort
+		 * during execution.
+		 */
+		req->frameOptions = (FRAMEOPTION_ROWS |
+							 FRAMEOPTION_START_UNBOUNDED_PRECEDING |
+							 FRAMEOPTION_END_CURRENT_ROW);
+
+		PG_RETURN_POINTER(req);
+	}
+
 	PG_RETURN_POINTER(NULL);
 }
 
@@ -190,6 +227,22 @@ window_dense_rank_support(PG_FUNCTION_ARGS)
 		PG_RETURN_POINTER(req);
 	}
 
+	if (IsA(rawreq, SupportRequestOptimizeWindowClause))
+	{
+		SupportRequestOptimizeWindowClause *req = (SupportRequestOptimizeWindowClause *) rawreq;
+
+		/*
+		 * Like window_rank(), window_dense_rank() is also unaffected by the
+		 * frame options.  Here we just set them to match what's done for the
+		 * row_number() and rank() window functions.
+		 */
+		req->frameOptions = (FRAMEOPTION_ROWS |
+							 FRAMEOPTION_START_UNBOUNDED_PRECEDING |
+							 FRAMEOPTION_END_CURRENT_ROW);
+
+		PG_RETURN_POINTER(req);
+	}
+
 	PG_RETURN_POINTER(NULL);
 }
 
diff --git a/src/include/nodes/supportnodes.h b/src/include/nodes/supportnodes.h
index 9fcbc39949..b446125b2b 100644
--- a/src/include/nodes/supportnodes.h
+++ b/src/include/nodes/supportnodes.h
@@ -299,4 +299,48 @@ typedef struct SupportRequestWFuncMonotonic
 	MonotonicFunction monotonic;
 } SupportRequestWFuncMonotonic;
 
+/*
+ * Some WindowFunc behavior might not be affected by certain variations in
+ * the WindowClause's frameOptions.  For example, row_number() is coded in
+ * such a way that the frame options don't change the returned row number.
+ * nodeWindowAgg.c will have less work to do if the ROWS option is used
+ * instead of the RANGE option as no check needs to be done for peer rows.
+ * Since RANGE is included in the default frame options, window functions
+ * such as row_number() might want to change that to ROW.
+ *
+ * Here we allow a WindowFunc's support function to determine which, if
+ * anything, can be changed about the WindowClause which the WindowFunc
+ * belongs to.  Currently only the frameOptions can be modified.  However,
+ * we may want to allow more optimizations in the future.
+ *
+ * The support function is responsible for ensuring the optimized version of
+ * the frameOptions doesn't affect the result of the window function.  The
+ * planner is responsible for only changing the frame options when all
+ * WindowFuncs using this particular WindowClause agree on what the optimized
+ * version of the frameOptions are.  If a particular WindowFunc being used
+ * does not have a support function then the planner will not make any changes
+ * to the WindowClause's frameOptions.
+ *
+ * 'window_func' and 'window_clause' are set by the planner before calling the
+ * support function so that the support function has these fields available.
+ * These may be required in order to determine which optimizations are
+ * possible.
+ *
+ * 'frameOptions' is set by the planner to WindowClause.frameOptions.  The
+ * support function must only adjust this if optimizations are possible for
+ * the given WindowFunc.
+ */
+typedef struct SupportRequestOptimizeWindowClause
+{
+	NodeTag		type;
+
+	/* Input fields: */
+	WindowFunc *window_func;	/* Pointer to the window function data */
+	struct WindowClause *window_clause; /* Pointer to the window clause data */
+
+	/* Input/Output fields: */
+	int			frameOptions;	/* New frameOptions, or left untouched if no
+								 * optimizations are possible. */
+} SupportRequestOptimizeWindowClause;
+
 #endif							/* SUPPORTNODES_H */