Fix missing outfuncs.c support for IncrementalSortPath.

For debugging purposes, Path nodes are supposed to have outfuncs
support, but this was overlooked in the original incremental sort patch.

While at it, clean up a couple other minor oversights, as well as
bizarre choice of return type for create_incremental_sort_path().
(All the existing callers just cast it to "Path *" immediately, so
they don't care, but some future caller might care.)

outfuncs.c fix by Zhijie Hou, the rest by me

Discussion: https://postgr.es/m/324c4d81d8134117972a5b1f6cdf9560@G08CNEXMBPEKD05.g08.fujitsu.local

5 files changed, 34 insertions, 11 deletions

diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index e2f177515da..07c93b4737a 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -1955,13 +1955,29 @@ _outProjectSetPath(StringInfo str, const ProjectSetPath *node)
 }
 
 static void
+_outSortPathInfo(StringInfo str, const SortPath *node)
+{
+	_outPathInfo(str, (const Path *) node);
+
+	WRITE_NODE_FIELD(subpath);
+}
+
+static void
 _outSortPath(StringInfo str, const SortPath *node)
 {
 	WRITE_NODE_TYPE("SORTPATH");
 
-	_outPathInfo(str, (const Path *) node);
+	_outSortPathInfo(str, node);
+}
 
-	WRITE_NODE_FIELD(subpath);
+static void
+_outIncrementalSortPath(StringInfo str, const IncrementalSortPath *node)
+{
+	WRITE_NODE_TYPE("INCREMENTALSORTPATH");
+
+	_outSortPathInfo(str, (const SortPath *) node);
+
+	WRITE_INT_FIELD(nPresortedCols);
 }
 
 static void
@@ -4058,6 +4074,9 @@ outNode(StringInfo str, const void *obj)
 			case T_SortPath:
 				_outSortPath(str, obj);
 				break;
+			case T_IncrementalSortPath:
+				_outIncrementalSortPath(str, obj);
+				break;
 			case T_GroupPath:
 				_outGroupPath(str, obj);
 				break;
diff --git a/src/backend/optimizer/README b/src/backend/optimizer/README
index d174b8cb73a..efb52858c88 100644
--- a/src/backend/optimizer/README
+++ b/src/backend/optimizer/README
@@ -387,6 +387,7 @@ RelOptInfo      - a relation or joined relations
   ProjectionPath - a Result plan node with child (used for projection)
   ProjectSetPath - a ProjectSet plan node applied to some sub-path
   SortPath      - a Sort plan node applied to some sub-path
+  IncrementalSortPath - an IncrementalSort plan node applied to some sub-path
   GroupPath     - a Group plan node applied to some sub-path
   UpperUniquePath - a Unique plan node applied to some sub-path
   AggPath       - an Agg plan node applied to some sub-path
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index c1fc866cbf9..5778f80c01e 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -2798,7 +2798,7 @@ create_set_projection_path(PlannerInfo *root,
  * 'limit_tuples' is the estimated bound on the number of output tuples,
  *		or -1 if no LIMIT or couldn't estimate
  */
-SortPath *
+IncrementalSortPath *
 create_incremental_sort_path(PlannerInfo *root,
 							 RelOptInfo *rel,
 							 Path *subpath,
@@ -2834,7 +2834,7 @@ create_incremental_sort_path(PlannerInfo *root,
 
 	sort->nPresortedCols = presorted_keys;
 
-	return pathnode;
+	return sort;
 }
 
 /*
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index 8d1ad3339f2..10f0a149e91 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -1650,7 +1650,10 @@ typedef struct SortPath
 } SortPath;
 
 /*
- * IncrementalSortPath
+ * IncrementalSortPath represents an incremental sort step
+ *
+ * This is like a regular sort, except some leading key columns are assumed
+ * to be ordered already.
  */
 typedef struct IncrementalSortPath
 {
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index 715a24ad29a..3bd7072ae8c 100644
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -184,17 +184,17 @@ extern ProjectSetPath *create_set_projection_path(PlannerInfo *root,
 												  RelOptInfo *rel,
 												  Path *subpath,
 												  PathTarget *target);
-extern SortPath *create_incremental_sort_path(PlannerInfo *root,
-											  RelOptInfo *rel,
-											  Path *subpath,
-											  List *pathkeys,
-											  int presorted_keys,
-											  double limit_tuples);
 extern SortPath *create_sort_path(PlannerInfo *root,
 								  RelOptInfo *rel,
 								  Path *subpath,
 								  List *pathkeys,
 								  double limit_tuples);
+extern IncrementalSortPath *create_incremental_sort_path(PlannerInfo *root,
+														 RelOptInfo *rel,
+														 Path *subpath,
+														 List *pathkeys,
+														 int presorted_keys,
+														 double limit_tuples);
 extern GroupPath *create_group_path(PlannerInfo *root,
 									RelOptInfo *rel,
 									Path *subpath,