Reimplement planner's handling of MIN/MAX aggregate optimization (again).

Instead of playing cute games with pathkeys, just build a direct
representation of the intended sub-select, and feed it through
query_planner to get a Path for the index access.  This is a bit slower
than 9.1's previous method, since we'll duplicate most of the overhead of
query_planner; but since the whole optimization only applies to rather
simple single-table queries, that probably won't be much of a problem in
practice.  The advantage is that we get to do the right thing when there's
a partial index that needs the implicit IS NOT NULL clause to be usable.
Also, although this makes planagg.c be a bit more closely tied to the
ordering of operations in grouping_planner, we can get rid of some coupling
to lower-level parts of the planner.  Per complaint from Marti Raudsepp.

3 files changed, 4 insertions, 34 deletions

diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 6e52d36a17e..b903e457a0b 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -1930,22 +1930,6 @@ _copyPlaceHolderInfo(PlaceHolderInfo *from)
 	return newnode;
 }
 
-/*
- * _copyMinMaxAggInfo
- */
-static MinMaxAggInfo *
-_copyMinMaxAggInfo(MinMaxAggInfo *from)
-{
-	MinMaxAggInfo *newnode = makeNode(MinMaxAggInfo);
-
-	COPY_SCALAR_FIELD(aggfnoid);
-	COPY_SCALAR_FIELD(aggsortop);
-	COPY_NODE_FIELD(target);
-	COPY_NODE_FIELD(pathkeys);
-
-	return newnode;
-}
-
 /* ****************************************************************
  *					parsenodes.h copy functions
  * ****************************************************************
@@ -4129,9 +4113,6 @@ copyObject(void *from)
 		case T_PlaceHolderInfo:
 			retval = _copyPlaceHolderInfo(from);
 			break;
-		case T_MinMaxAggInfo:
-			retval = _copyMinMaxAggInfo(from);
-			break;
 
 			/*
 			 * VALUE NODES
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 7340aa05251..10b160f537e 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -886,17 +886,6 @@ _equalPlaceHolderInfo(PlaceHolderInfo *a, PlaceHolderInfo *b)
 	return true;
 }
 
-static bool
-_equalMinMaxAggInfo(MinMaxAggInfo *a, MinMaxAggInfo *b)
-{
-	COMPARE_SCALAR_FIELD(aggfnoid);
-	COMPARE_SCALAR_FIELD(aggsortop);
-	COMPARE_NODE_FIELD(target);
-	COMPARE_NODE_FIELD(pathkeys);
-
-	return true;
-}
-
 
 /*
  * Stuff from parsenodes.h
@@ -2690,9 +2679,6 @@ equal(void *a, void *b)
 		case T_PlaceHolderInfo:
 			retval = _equalPlaceHolderInfo(a, b);
 			break;
-		case T_MinMaxAggInfo:
-			retval = _equalMinMaxAggInfo(a, b);
-			break;
 
 		case T_List:
 		case T_IntList:
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index db4a33c30d1..46435ab21c3 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -1914,7 +1914,10 @@ _outMinMaxAggInfo(StringInfo str, MinMaxAggInfo *node)
 	WRITE_OID_FIELD(aggfnoid);
 	WRITE_OID_FIELD(aggsortop);
 	WRITE_NODE_FIELD(target);
-	WRITE_NODE_FIELD(pathkeys);
+	/* We intentionally omit subroot --- too large, not interesting enough */
+	WRITE_NODE_FIELD(path);
+	WRITE_FLOAT_FIELD(pathcost, "%.2f");
+	WRITE_NODE_FIELD(param);
 }
 
 static void