v29-0002-Modify-merge_null_partitions.patch

From 9d00b41479b7bc172e25b776ee93d066e011061f Mon Sep 17 00:00:00 2001
From: Amul Sul <amul.sul@enterprisedb.com>
Date: Mon, 9 Dec 2019 04:07:54 -0500
Subject: [PATCH 2/2] v29-0002-Modify-merge_null_partitions

---
 src/backend/partitioning/partbounds.c        | 490 ++++++++++---------
 src/test/regress/expected/partition_join.out | 292 ++++++-----
 src/test/regress/sql/partition_join.sql      |   5 +-
 3 files changed, 427 insertions(+), 360 deletions(-)

diff --git a/src/backend/partitioning/partbounds.c b/src/backend/partitioning/partbounds.c
index a362998e574..494632fc7c7 100644
--- a/src/backend/partitioning/partbounds.c
+++ b/src/backend/partitioning/partbounds.c
@@ -141,7 +141,7 @@ static int map_and_merge_partitions(PartitionMap *outer_map, PartitionMap *inner
 						 int outer_part, int inner_part, int *next_index);
 static int merge_partition_with_dummy(PartitionMap *map, int index,
 						   int *next_index);
-static bool process_outer_partition(PartitionMap *outer_map,
+static int process_outer_partition(PartitionMap *outer_map,
 						PartitionMap *inner_map,
 						bool outer_has_default,
 						bool inner_has_default,
@@ -149,9 +149,8 @@ static bool process_outer_partition(PartitionMap *outer_map,
 						int inner_default,
 						JoinType jointype,
 						int *next_index,
-						int *default_index,
-						int *merged_index);
-static bool process_inner_partition(PartitionMap *outer_map,
+						int *default_index);
+static int process_inner_partition(PartitionMap *outer_map,
 						PartitionMap *inner_map,
 						bool outer_has_default,
 						bool inner_has_default,
@@ -159,8 +158,7 @@ static bool process_inner_partition(PartitionMap *outer_map,
 						int outer_default,
 						JoinType jointype,
 						int *next_index,
-						int *default_index,
-						int *merged_index);
+						int *default_index);
 static void fix_merged_indexes(PartitionMap *outer_map, PartitionMap *inner_map,
 				   int nmerged, List *merged_indexes);
 static void generate_matching_part_pairs(RelOptInfo *outer_rel,
@@ -200,21 +198,24 @@ static void add_merged_range_bounds(int partnatts, FmgrInfo *partsupfuncs,
 						List **merged_datums,
 						List **merged_kinds,
 						List **merged_indexes);
-static bool merge_default_partitions(PartitionMap *outer_map,
+static void merge_default_partitions(PartitionMap *outer_map,
 						 PartitionMap *inner_map,
 						 bool outer_has_default,
-						 int outer_default,
 						 bool inner_has_default,
+						 int outer_default,
 						 int inner_default,
 						 JoinType jointype,
 						 int *next_index,
 						 int *default_index);
-static bool merge_null_partitions(PartitionBoundInfo outer_bi, PartitionBoundInfo inner_bi,
-					  PartitionMap *outer_map, PartitionMap *inner_map,
-					  bool outer_has_default, bool inner_has_default,
-					  bool outer_has_null, bool inner_has_null,
-					  JoinType jointype, int *next_index,
-					  int *default_index, int *null_index);
+static void merge_null_partitions(PartitionMap *outer_map,
+					  PartitionMap *inner_map,
+					  bool outer_has_null,
+					  bool inner_has_null,
+					  int outer_null,
+					  int inner_null,
+					  JoinType jointype,
+					  int *next_index,
+					  int *null_index);
 
 /*
  * get_qual_from_partbound
@@ -3554,11 +3555,11 @@ partition_range_bounds_merge(int partnatts, FmgrInfo *partsupfuncs,
 			if (ub_cmpval > 0 && inner_part >= 0 &&
 				compare_range_bounds(partnatts, partsupfuncs, partcollations,
 									 &save_outer_ub, &inner_lb) > 0)
-				return NULL;
+				goto cleanup;
 			if (ub_cmpval < 0 && outer_part >= 0 &&
 				compare_range_bounds(partnatts, partsupfuncs, partcollations,
 									 &outer_lb, &save_inner_ub) < 0)
-				return NULL;
+				goto cleanup;
 
 			/*
 			 * A row from a non-overlapping portion (if any) of a partition
@@ -3568,7 +3569,7 @@ partition_range_bounds_merge(int partnatts, FmgrInfo *partsupfuncs,
 			 */
 			if ((outer_has_default && (lb_cmpval > 0 || ub_cmpval < 0)) ||
 				(inner_has_default && (lb_cmpval < 0 || ub_cmpval > 0)))
-				return NULL;
+				goto cleanup;
 		}
 		else if (ub_cmpval < 0)
 		{
@@ -3579,17 +3580,17 @@ partition_range_bounds_merge(int partnatts, FmgrInfo *partsupfuncs,
 
 			if (inner_has_default || IS_OUTER_JOIN(jointype))
 			{
-				if (!process_outer_partition(&outer_map,
-											 &inner_map,
-											 outer_has_default,
-											 inner_has_default,
-											 outer_part,
-											 inner_default,
-											 jointype,
-											 &next_index,
-											 &default_index,
-											 &merged_index))
-					return NULL;
+				merged_index = process_outer_partition(&outer_map,
+													   &inner_map,
+													   outer_has_default,
+													   inner_has_default,
+													   outer_part,
+													   inner_default,
+													   jointype,
+													   &next_index,
+													   &default_index);
+				if (merged_index == -1)
+					goto cleanup;
 			}
 
 			/* Move to the next partition on the outer side. */
@@ -3606,17 +3607,17 @@ partition_range_bounds_merge(int partnatts, FmgrInfo *partsupfuncs,
 
 			if (outer_has_default || jointype == JOIN_FULL)
 			{
-				if (!process_inner_partition(&outer_map,
-											 &inner_map,
-											 outer_has_default,
-											 inner_has_default,
-											 inner_part,
-											 outer_default,
-											 jointype,
-											 &next_index,
-											 &default_index,
-											 &merged_index))
-					return NULL;
+				merged_index = process_inner_partition(&outer_map,
+													   &inner_map,
+													   outer_has_default,
+													   inner_has_default,
+													   inner_part,
+													   outer_default,
+													   jointype,
+													   &next_index,
+													   &default_index);
+				if (merged_index == -1)
+					goto cleanup;
 			}
 
 			/* Move to the next partition on the inner side. */
@@ -3624,7 +3625,7 @@ partition_range_bounds_merge(int partnatts, FmgrInfo *partsupfuncs,
 											 &inner_lb, &inner_ub);
 		}
 
-		if (merged_index >= 0)
+		if (merged_index >= 0 && merged_index != default_index)
 		{
 			/* Add the range bounds of the merged partition. */
 			add_merged_range_bounds(partnatts, partsupfuncs, partcollations,
@@ -3636,18 +3637,10 @@ partition_range_bounds_merge(int partnatts, FmgrInfo *partsupfuncs,
 
 	/* Merge default partitions if any. */
 	if (outer_has_default || inner_has_default)
-	{
-		if (!merge_default_partitions(&outer_map,
-									  &inner_map,
-									  outer_has_default,
-									  outer_default,
-									  inner_has_default,
-									  inner_default,
-									  jointype,
-									  &next_index,
-									  &default_index))
-			return NULL;
-	}
+		merge_default_partitions(&outer_map, &inner_map,
+								 outer_has_default, inner_has_default,
+								 outer_default, inner_default,
+								 jointype, &next_index, &default_index);
 	else
 		Assert(default_index == -1);
 
@@ -3675,7 +3668,8 @@ partition_range_bounds_merge(int partnatts, FmgrInfo *partsupfuncs,
 													  -1, default_index);
 	}
 
-	/* Free any memory we used in this function. */
+cleanup:
+	/* Free local memory before returning. */
 	free_partition_map(&outer_map);
 	free_partition_map(&inner_map);
 	list_free(merged_datums);
@@ -3789,8 +3783,8 @@ partition_list_bounds_merge(FmgrInfo *partsupfunc, Oid *partcollation,
 													o_index, i_index,
 													&next_index);
 
-			if (merged_index < 0)
-				return NULL;
+			if (merged_index == -1)
+				goto cleanup;
 
 			/* Move to the next pair of bounds. */
 			cnto++;
@@ -3808,17 +3802,17 @@ partition_list_bounds_merge(FmgrInfo *partsupfunc, Oid *partcollation,
 				int			o_index = outer_bi->indexes[cnto];
 
 				Assert(o_index >= 0);
-				if (!process_outer_partition(&outer_map,
-											 &inner_map,
-											 outer_has_default,
-											 inner_has_default,
-											 o_index,
-											 inner_default,
-											 jointype,
-											 &next_index,
-											 &default_index,
-											 &merged_index))
-					return NULL;
+				merged_index = process_outer_partition(&outer_map,
+													   &inner_map,
+													   outer_has_default,
+													   inner_has_default,
+													   o_index,
+													   inner_default,
+													   jointype,
+													   &next_index,
+													   &default_index);
+				if (merged_index == -1)
+					goto cleanup;
 			}
 
 			/* Move to the next datum on the outer side. */
@@ -3837,17 +3831,17 @@ partition_list_bounds_merge(FmgrInfo *partsupfunc, Oid *partcollation,
 				int			i_index = inner_bi->indexes[cnti];
 
 				Assert(i_index >= 0);
-				if (!process_inner_partition(&outer_map,
-											 &inner_map,
-											 outer_has_default,
-											 inner_has_default,
-											 i_index,
-											 outer_default,
-											 jointype,
-											 &next_index,
-											 &default_index,
-											 &merged_index))
-					return NULL;
+				merged_index = process_inner_partition(&outer_map,
+													   &inner_map,
+													   outer_has_default,
+													   inner_has_default,
+													   i_index,
+													   outer_default,
+													   jointype,
+													   &next_index,
+													   &default_index);
+				if (merged_index == -1)
+					goto cleanup;
 			}
 
 			/* Move to the next datum on the inner side. */
@@ -3858,7 +3852,7 @@ partition_list_bounds_merge(FmgrInfo *partsupfunc, Oid *partcollation,
 		 * Add the list value with appropriate index in the list of datums, if
 		 * we have associated a partition with this list value.
 		 */
-		if (merged_index >= 0)
+		if (merged_index >= 0 && merged_index != default_index)
 		{
 			merged_indexes = lappend_int(merged_indexes, merged_index);
 			merged_datums = lappend(merged_datums, merged_datum);
@@ -3867,27 +3861,19 @@ partition_list_bounds_merge(FmgrInfo *partsupfunc, Oid *partcollation,
 
 	/* Merge null partitions if any. */
 	if (outer_has_null || inner_has_null)
-	{
-		if (!merge_null_partitions(outer_bi, inner_bi,
-								   &outer_map, &inner_map,
-								   outer_has_default, inner_has_default,
-								   outer_has_null, inner_has_null,
-								   jointype, &next_index, &default_index,
-								   &null_index))
-			return NULL;
-	}
+		merge_null_partitions(&outer_map, &inner_map,
+							  outer_has_null, inner_has_null,
+							  outer_bi->null_index, inner_bi->null_index,
+							  jointype, &next_index, &null_index);
 	else
 		Assert(null_index == -1);
 
 	/* Merge default partitions if any. */
 	if (outer_has_default || inner_has_default)
-	{
-		if (!merge_default_partitions(&outer_map, &inner_map,
-									  outer_has_default, outer_default,
-									  inner_has_default, inner_default,
-									  jointype, &next_index, &default_index))
-			return NULL;
-	}
+		merge_default_partitions(&outer_map, &inner_map,
+								 outer_has_default, inner_has_default,
+								 outer_default, inner_default,
+								 jointype, &next_index, &default_index);
 	else
 		Assert(default_index == -1);
 
@@ -3916,7 +3902,8 @@ partition_list_bounds_merge(FmgrInfo *partsupfunc, Oid *partcollation,
 													  null_index, default_index);
 	}
 
-	/* Free up all extra memory before returning from this function. */
+cleanup:
+	/* Free local memory before returning. */
 	free_partition_map(&outer_map);
 	free_partition_map(&inner_map);
 	list_free(merged_datums);
@@ -4099,7 +4086,7 @@ merge_partition_with_dummy(PartitionMap *map, int index, int *next_index)
  * *next_index is incremented when creating a new merged partition associated
  * with the given outer partition.
  */
-static bool
+static int
 process_outer_partition(PartitionMap *outer_map,
 						PartitionMap *inner_map,
 						bool outer_has_default,
@@ -4108,9 +4095,10 @@ process_outer_partition(PartitionMap *outer_map,
 						int inner_default,
 						JoinType jointype,
 						int *next_index,
-						int *default_index,
-						int *merged_index)
+						int *default_index)
 {
+	int 		merged_index = -1;
+
 	Assert(outer_index >= 0);
 
 	/*
@@ -4131,13 +4119,13 @@ process_outer_partition(PartitionMap *outer_map,
 		 * up on it.
 		 */
 		if (outer_has_default)
-			return false;
+			return -1;
 
-		*merged_index = map_and_merge_partitions(outer_map, inner_map,
-												 outer_index, inner_default,
-												 next_index);
-		if (*merged_index == -1)
-			return false;
+		merged_index = map_and_merge_partitions(outer_map, inner_map,
+												outer_index, inner_default,
+												next_index);
+		if (merged_index == -1)
+			return -1;
 
 		/*
 		 * If this is a FULL join, the merged partition would act as the
@@ -4147,11 +4135,9 @@ process_outer_partition(PartitionMap *outer_map,
 		if (jointype == JOIN_FULL)
 		{
 			if (*default_index == -1)
-				*default_index = *merged_index;
+				*default_index = merged_index;
 			else
-				Assert(*merged_index == *default_index);
-			/* Don't add this index to the list of merged indexes. */
-			*merged_index = -1;
+				Assert(*default_index == merged_index);
 		}
 	}
 	else
@@ -4159,13 +4145,12 @@ process_outer_partition(PartitionMap *outer_map,
 		Assert(IS_OUTER_JOIN(jointype));
 		Assert(jointype != JOIN_RIGHT);
 
-		if (outer_map->merged_indexes[outer_index] >= 0)
-			*merged_index = outer_map->merged_indexes[outer_index];
-		else
-			*merged_index = merge_partition_with_dummy(outer_map, outer_index,
-													   next_index);
+		merged_index = outer_map->merged_indexes[outer_index];
+		if (merged_index == -1)
+			merged_index = merge_partition_with_dummy(outer_map, outer_index,
+													  next_index);
 	}
-	return true;
+	return merged_index;
 }
 
 /*
@@ -4176,7 +4161,7 @@ process_outer_partition(PartitionMap *outer_map,
  * *next_index is incremented when creating a new merged partition associated
  * with the given inner partition.
  */
-static bool
+static int
 process_inner_partition(PartitionMap *outer_map,
 						PartitionMap *inner_map,
 						bool outer_has_default,
@@ -4185,9 +4170,10 @@ process_inner_partition(PartitionMap *outer_map,
 						int outer_default,
 						JoinType jointype,
 						int *next_index,
-						int *default_index,
-						int *merged_index)
+						int *default_index)
 {
+	int 		merged_index = -1;
+
 	Assert(inner_index >= 0);
 
 	/*
@@ -4208,13 +4194,13 @@ process_inner_partition(PartitionMap *outer_map,
 		 * up on it.
 		 */
 		if (inner_has_default)
-			return false;
+			return -1;
 
-		*merged_index = map_and_merge_partitions(outer_map, inner_map,
-												 outer_default, inner_index,
-												 next_index);
-		if (*merged_index == -1)
-			return false;
+		merged_index = map_and_merge_partitions(outer_map, inner_map,
+												outer_default, inner_index,
+												next_index);
+		if (merged_index == -1)
+			return -1;
 
 		/*
 		 * If this is an outer join, the merged partition would act as the
@@ -4225,24 +4211,21 @@ process_inner_partition(PartitionMap *outer_map,
 		{
 			Assert(jointype != JOIN_RIGHT);
 			if (*default_index == -1)
-				*default_index = *merged_index;
+				*default_index = merged_index;
 			else
-				Assert(*merged_index == *default_index);
-			/* Don't add this index to the list of merged indexes. */
-			*merged_index = -1;
+				Assert(*default_index == merged_index);
 		}
 	}
 	else
 	{
 		Assert(jointype == JOIN_FULL);
 
-		if (inner_map->merged_indexes[inner_index] >= 0)
-			*merged_index = inner_map->merged_indexes[inner_index];
-		else
-			*merged_index = merge_partition_with_dummy(inner_map, inner_index,
-													   next_index);
+		merged_index = inner_map->merged_indexes[inner_index];
+		if (merged_index == -1)
+			merged_index = merge_partition_with_dummy(inner_map, inner_index,
+													  next_index);
 	}
-	return true;
+	return merged_index;
 }
 
 /*
@@ -4430,175 +4413,200 @@ build_merged_partition_bounds(char strategy, List *merged_datums,
 }
 
 /*
- * Merge default partitions from both sides, if any, and assign the default
- * partition for the join result, if necessary.
- *
- * If both the relations have default partitions, try mapping those to each
- * other. If the mapping succeeds corresponding merged partition will act as
- * the default partition of the join result.
+ * merge_default_partitions
+ *		Merge the default partitions from both sides, if any
  *
- * If inner side of the join has default but not the outer side, rows in it
- * won't appear in the join result. So don't create a default partition. If
- * outer side of the join has default but not the inner side, rows in it will
- * appear in the join result, so create a default merged partition.
+ * *default_index is set to the index of the default partition of the joinrel,
+ * if appropriate.
  */
-static bool
-merge_default_partitions(PartitionMap *outer_map, PartitionMap *inner_map,
-						 bool outer_has_default, int outer_default,
-						 bool inner_has_default, int inner_default,
-						 JoinType jointype, int *next_index,
+static void
+merge_default_partitions(PartitionMap *outer_map,
+						 PartitionMap *inner_map,
+						 bool outer_has_default,
+						 bool inner_has_default,
+						 int outer_default,
+						 int inner_default,
+						 JoinType jointype,
+						 int *next_index,
 						 int *default_index)
 {
+	int 		outer_merged_index = -1;
+	int 		inner_merged_index = -1;
+
 	Assert(outer_has_default || inner_has_default);
 
+	if (outer_has_default)
+	{
+		Assert(outer_default >= 0 && outer_default < outer_map->nparts);
+		outer_merged_index = outer_map->merged_indexes[outer_default];
+	}
+	if (inner_has_default)
+	{
+		Assert(inner_default >= 0 && inner_default < inner_map->nparts);
+		inner_merged_index = inner_map->merged_indexes[inner_default];
+	}
+
 	if (outer_has_default && !inner_has_default)
 	{
+		/*
+		 * If this is an outer join, assign a new merged partition if not
+		 * already done.  The resulting partition should be the default
+		 * partition of the joinrel.
+		 */
 		if (IS_OUTER_JOIN(jointype))
 		{
-			int			merged_index;
-
 			Assert(jointype != JOIN_RIGHT);
-			Assert(outer_default >= 0 && outer_default < outer_map->nparts);
-			merged_index = outer_map->merged_indexes[outer_default];
-			if (merged_index == -1)
-			{
-				Assert(*default_index == -1);
+			if (outer_merged_index == -1)
 				*default_index = merge_partition_with_dummy(outer_map,
 															outer_default,
 															next_index);
-			}
 			else
-				Assert(*default_index == merged_index);
+				Assert(*default_index == outer_merged_index);
 		}
 		else
-			Assert(*default_index < 0);
+			Assert(*default_index == -1);
 	}
 	else if (!outer_has_default && inner_has_default)
 	{
+		/*
+		 * If this is a FULL join, assign a new merged partition if not
+		 * already done.  The resulting partition should be the default
+		 * partition of the joinrel.
+		 */
 		if (jointype == JOIN_FULL)
 		{
-			int			merged_index;
-
-			Assert(inner_default >= 0 && inner_default < inner_map->nparts);
-			merged_index = inner_map->merged_indexes[inner_default];
-			if (merged_index == -1)
-			{
-				Assert(*default_index == -1);
+			if (inner_merged_index == -1)
 				*default_index = merge_partition_with_dummy(inner_map,
 															inner_default,
 															next_index);
-			}
 			else
-				Assert(*default_index == merged_index);
+				Assert(*default_index == inner_merged_index);
 		}
 		else
-			Assert(*default_index < 0);
+			Assert(*default_index == -1);
 	}
 	else
 	{
 		Assert(outer_has_default && inner_has_default);
+		Assert(outer_merged_index == -1);
+		Assert(inner_merged_index == -1);
+		Assert(*default_index == -1);
 
+		/*
+		 * Merge the default partitions.  Both partitions aren't merged yet,
+		 * so the partitions should be merged successfully.  The resulting
+		 * partition should be the default partition of the joinrel.
+		 */
 		*default_index = map_and_merge_partitions(outer_map,
 												  inner_map,
 												  outer_default,
 												  inner_default,
 												  next_index);
-		if (*default_index == -1)
-			return false;
+		Assert(*default_index >= 0);
 	}
-
-	return true;
 }
 
 /*
  * merge_null_partitions
+ *		Merge the NULL partitions from both sides, if any
  *
- * Merge NULL partitions, i.e. a partition that can hold NULL values for a list
- * partitioned table, if any. Find the index of merged partition to which the
- * NULL values would belong in the join result. If one joining relation has a
- * NULL partition but not the other, try matching it with the default partition
- * from the other relation since the default partition may have rows with NULL
- * partition key. We can eliminate a NULL partition when it appears only on the
- * inner side of the join and the outer side doesn't have a default partition.
- *
- * When the equality operator used for join is strict, two NULL values will not
- * be considered as equal, and thus a NULL partition can be eliminated for an
- * inner join. But we don't check the strictness operator here.
+ * *null_index is set to the index of the NULL partition of the joinrel, if
+ * appropriate.
  */
-static bool
-merge_null_partitions(PartitionBoundInfo outer_bi, PartitionBoundInfo inner_bi,
-					  PartitionMap *outer_map, PartitionMap *inner_map,
-					  bool outer_has_default, bool inner_has_default,
-					  bool outer_has_null, bool inner_has_null,
-					  JoinType jointype, int *next_index,
-					  int *default_index, int *null_index)
+static void
+merge_null_partitions(PartitionMap *outer_map,
+					  PartitionMap *inner_map,
+					  bool outer_has_null,
+					  bool inner_has_null,
+					  int outer_null,
+					  int inner_null,
+					  JoinType jointype,
+					  int *next_index,
+					  int *null_index)
 {
+	bool 		merge_outer_null = false;
+	bool 		merge_inner_null = false;
+
 	Assert(outer_has_null || inner_has_null);
 	Assert(*null_index == -1);
 
-	if (outer_has_null && !inner_has_null)
+	/*
+	 * If this is an INNER or SEMI join, two NULL values won't be considered
+	 * to be equal, in which case we don't need to do anything.
+	 */
+	if (jointype == JOIN_INNER || jointype == JOIN_SEMI)
+		return;
+
+	Assert(IS_OUTER_JOIN(jointype));
+	Assert(jointype != JOIN_RIGHT);
+
+	if (outer_has_null)
 	{
-		int			merged_index = -1;
+		/*
+		 * Since this is an outer join, if the NULL partition of the outer
+		 * side isn't merged yet, it means that the partition contains only
+		 * NULL values as the key values, in which case we need to create a
+		 * merged partition below.
+		 */
+		Assert(outer_null >= 0 && outer_null < outer_map->nparts);
+		if (outer_map->merged_indexes[outer_null] == -1)
+			merge_outer_null = true;
+	}
+	if (inner_has_null)
+	{
+		/*
+		 * If this is a FULL join, and the NULL partition of the inner side
+		 * isn't merged yet, it means that the partition contains only NULL
+		 * values as the key values, in which case we need to create a merged
+		 * partition below.
+		 */
+		Assert(inner_null >= 0 && inner_null < inner_map->nparts);
+		if (jointype == JOIN_FULL &&
+			inner_map->merged_indexes[inner_null] == -1)
+			merge_inner_null = true;
+	}
+
+	if (!merge_outer_null && !merge_inner_null)
+		return;
+
+	if (merge_outer_null && !merge_inner_null)
+	{
+		Assert(outer_has_null);
 
 		/*
-		 * If the NULL partition was missing from the inner side of the join,
-		 * the partition of the join to which the NULL partition matches will
-		 * contain the NULL values and thus become the NULL partition of the
-		 * the join.
+		 * Assign a new merged partition.  The resulting partition should be
+		 * the NULL partition of the joinrel.
 		 */
-		if (inner_has_default || IS_OUTER_JOIN(jointype))
-		{
-			if (!process_outer_partition(outer_map,
-										 inner_map,
-										 outer_has_default,
-										 inner_has_default,
-										 outer_bi->null_index,
-										 inner_bi->default_index,
-										 jointype,
-										 next_index,
-										 default_index,
-										 &merged_index))
-				return false;
-		}
-		*null_index = merged_index;
+		*null_index = merge_partition_with_dummy(outer_map, outer_null,
+												 next_index);
 	}
-	else if (!outer_has_null && inner_has_null)
+	else if (!merge_outer_null && merge_inner_null)
 	{
-		int			merged_index = -1;
+		Assert(inner_has_null);
+		Assert(jointype == JOIN_FULL);
 
 		/*
-		 * If the NULL partition was missing from the outer side of the join,
-		 * the partition of the join to which the NULL partition matches will
-		 * contain the NULL values and thus become the NULL partition of the
-		 * the join.
+		 * Assign a new merged partition.  The resulting partition should be
+		 * the NULL partition of the joinrel.
 		 */
-		if (outer_has_default || jointype == JOIN_FULL)
-		{
-			if (!process_inner_partition(outer_map,
-										 inner_map,
-										 outer_has_default,
-										 inner_has_default,
-										 inner_bi->null_index,
-										 outer_bi->default_index,
-										 jointype,
-										 next_index,
-										 default_index,
-										 &merged_index))
-				return false;
-		}
-		*null_index = merged_index;
+		*null_index = merge_partition_with_dummy(inner_map, inner_null,
+												 next_index);
 	}
 	else
 	{
-		/* Both the relations have NULL partitions, try merging them. */
-		*null_index = map_and_merge_partitions(outer_map,
-											   inner_map,
-											   outer_bi->null_index,
-											   inner_bi->null_index,
+		Assert(merge_outer_null && merge_inner_null);
+		Assert(outer_has_null);
+		Assert(inner_has_null);
+		Assert(jointype == JOIN_FULL);
+
+		/*
+		 * Merge the NULL partitions.  Both partitions aren't merged yet, so
+		 * the partitions should be merged successfully.  The resulting
+		 * partition should be the NULL partition of the joinrel.
+		 */
+		*null_index = map_and_merge_partitions(outer_map, inner_map,
+											   outer_null, inner_null,
 											   next_index);
-		if (*null_index == -1)
-			return false;
+		Assert(*null_index >= 0);
 	}
-
-	return true;
 }
diff --git a/src/test/regress/expected/partition_join.out b/src/test/regress/expected/partition_join.out
index 815a6c90749..01fe9278cc9 100644
--- a/src/test/regress/expected/partition_join.out
+++ b/src/test/regress/expected/partition_join.out
@@ -3866,10 +3866,7 @@ select t1.a, t1.b, t1.c from plt2 t1 where not exists (select 1 from plt1 t2 WHE
  470 | 0 | 
 (1 row)
 
--- partition have a NULL on both side with different partition bounds w.r.t other side
--- NULL when NULL comparision is not strict i.e. NULL=NULL allowed
--- Partition-wise join can not handle the case when one partition from one side
--- matches with multiple partitions on the other side
+-- test the null-partition handling in the new partition-matching algorithm
 DROP TABLE plt1_p3;
 CREATE TABLE plt1_p3 PARTITION OF plt1 FOR VALUES IN (NULL,'0008','0009');
 INSERT INTO plt1 SELECT i, i % :cond_mod, case when i % :part_mod = 7 then NULL else to_char(i % :part_mod, 'FM0000') end FROM generate_series(0, :num_rows) i WHERE i % :part_mod IN (7,8,9);
@@ -3877,94 +3874,138 @@ ANALYZE plt1;
 -- inner join
 EXPLAIN (COSTS OFF)
 SELECT t1.a, t1.c, t2.a, t2.c FROM plt1 t1 INNER JOIN plt2 t2 ON t1.c = t2.c WHERE t1.b + t2.b = 0 ORDER BY t1.a;
-                    QUERY PLAN                    
---------------------------------------------------
+                         QUERY PLAN                         
+------------------------------------------------------------
  Sort
    Sort Key: t1.a
-   ->  Hash Join
-         Hash Cond: ((t2.c)::text = (t1.c)::text)
-         Join Filter: ((t1.b + t2.b) = 0)
-         ->  Append
+   ->  Append
+         ->  Hash Join
+               Hash Cond: ((t2.c)::text = (t1.c)::text)
+               Join Filter: ((t1.b + t2.b) = 0)
                ->  Seq Scan on plt2_p4 t2
-               ->  Seq Scan on plt2_p1 t2_1
-               ->  Seq Scan on plt2_p2 t2_2
-               ->  Seq Scan on plt2_p3 t2_3
-         ->  Hash
-               ->  Append
+               ->  Hash
                      ->  Seq Scan on plt1_p4 t1
+         ->  Hash Join
+               Hash Cond: ((t2_1.c)::text = (t1_1.c)::text)
+               Join Filter: ((t1_1.b + t2_1.b) = 0)
+               ->  Seq Scan on plt2_p1 t2_1
+               ->  Hash
                      ->  Seq Scan on plt1_p1 t1_1
-                     ->  Seq Scan on plt1_p2 t1_2
-                     ->  Seq Scan on plt1_p3 t1_3
-(16 rows)
+         ->  Hash Join
+               Hash Cond: ((t1_2.c)::text = (t2_2.c)::text)
+               Join Filter: ((t1_2.b + t2_2.b) = 0)
+               ->  Seq Scan on plt1_p2 t1_2
+               ->  Hash
+                     ->  Seq Scan on plt2_p2 t2_2
+         ->  Hash Join
+               Hash Cond: ((t1_3.c)::text = (t2_3.c)::text)
+               Join Filter: ((t1_3.b + t2_3.b) = 0)
+               ->  Seq Scan on plt1_p3 t1_3
+               ->  Hash
+                     ->  Seq Scan on plt2_p3 t2_3
+(27 rows)
 
 -- left join
 EXPLAIN (COSTS OFF)
 SELECT t1.a, t1.c, t2.a, t2.c FROM plt1 t1 LEFT JOIN plt2 t2 ON t1.c = t2.c WHERE t1.b + coalesce(t2.b, 0) = 0 ORDER BY t1.a;
-                    QUERY PLAN                    
---------------------------------------------------
+                         QUERY PLAN                         
+------------------------------------------------------------
  Sort
    Sort Key: t1.a
-   ->  Hash Right Join
-         Hash Cond: ((t2.c)::text = (t1.c)::text)
-         Filter: ((t1.b + COALESCE(t2.b, 0)) = 0)
-         ->  Append
+   ->  Append
+         ->  Hash Right Join
+               Hash Cond: ((t2.c)::text = (t1.c)::text)
+               Filter: ((t1.b + COALESCE(t2.b, 0)) = 0)
                ->  Seq Scan on plt2_p4 t2
-               ->  Seq Scan on plt2_p1 t2_1
-               ->  Seq Scan on plt2_p2 t2_2
-               ->  Seq Scan on plt2_p3 t2_3
-         ->  Hash
-               ->  Append
+               ->  Hash
                      ->  Seq Scan on plt1_p4 t1
+         ->  Hash Right Join
+               Hash Cond: ((t2_1.c)::text = (t1_1.c)::text)
+               Filter: ((t1_1.b + COALESCE(t2_1.b, 0)) = 0)
+               ->  Seq Scan on plt2_p1 t2_1
+               ->  Hash
                      ->  Seq Scan on plt1_p1 t1_1
-                     ->  Seq Scan on plt1_p2 t1_2
-                     ->  Seq Scan on plt1_p3 t1_3
-(16 rows)
+         ->  Hash Left Join
+               Hash Cond: ((t1_2.c)::text = (t2_2.c)::text)
+               Filter: ((t1_2.b + COALESCE(t2_2.b, 0)) = 0)
+               ->  Seq Scan on plt1_p2 t1_2
+               ->  Hash
+                     ->  Seq Scan on plt2_p2 t2_2
+         ->  Hash Left Join
+               Hash Cond: ((t1_3.c)::text = (t2_3.c)::text)
+               Filter: ((t1_3.b + COALESCE(t2_3.b, 0)) = 0)
+               ->  Seq Scan on plt1_p3 t1_3
+               ->  Hash
+                     ->  Seq Scan on plt2_p3 t2_3
+(27 rows)
 
 -- right join
 EXPLAIN (COSTS OFF)
 SELECT t1.a, t1.c, t2.a, t2.c FROM plt1 t1 RIGHT JOIN plt2 t2 ON t1.c = t2.c WHERE coalesce(t1.b, 0) + t2.b = 0 ORDER BY t2.a;
-                    QUERY PLAN                    
---------------------------------------------------
+                         QUERY PLAN                         
+------------------------------------------------------------
  Sort
    Sort Key: t2.a
-   ->  Hash Left Join
-         Hash Cond: ((t2.c)::text = (t1.c)::text)
-         Filter: ((COALESCE(t1.b, 0) + t2.b) = 0)
-         ->  Append
+   ->  Append
+         ->  Hash Left Join
+               Hash Cond: ((t2.c)::text = (t1.c)::text)
+               Filter: ((COALESCE(t1.b, 0) + t2.b) = 0)
                ->  Seq Scan on plt2_p4 t2
-               ->  Seq Scan on plt2_p1 t2_1
-               ->  Seq Scan on plt2_p2 t2_2
-               ->  Seq Scan on plt2_p3 t2_3
-         ->  Hash
-               ->  Append
+               ->  Hash
                      ->  Seq Scan on plt1_p4 t1
+         ->  Hash Left Join
+               Hash Cond: ((t2_1.c)::text = (t1_1.c)::text)
+               Filter: ((COALESCE(t1_1.b, 0) + t2_1.b) = 0)
+               ->  Seq Scan on plt2_p1 t2_1
+               ->  Hash
                      ->  Seq Scan on plt1_p1 t1_1
+         ->  Hash Left Join
+               Hash Cond: ((t2_2.c)::text = (t1_2.c)::text)
+               Filter: ((COALESCE(t1_2.b, 0) + t2_2.b) = 0)
+               ->  Seq Scan on plt2_p2 t2_2
+               ->  Hash
                      ->  Seq Scan on plt1_p2 t1_2
-                     ->  Seq Scan on plt1_p3 t1_3
-(16 rows)
+         ->  Hash Right Join
+               Hash Cond: ((t1_3.c)::text = (t2_3.c)::text)
+               Filter: ((COALESCE(t1_3.b, 0) + t2_3.b) = 0)
+               ->  Seq Scan on plt1_p3 t1_3
+               ->  Hash
+                     ->  Seq Scan on plt2_p3 t2_3
+(27 rows)
 
 -- full join
 EXPLAIN (COSTS OFF)
 SELECT t1.a, t1.c, t2.a, t2.c FROM plt1 t1 FULL JOIN plt2 t2 ON t1.c = t2.c WHERE coalesce(t1.b, 0) + coalesce(t2.b, 0) = 0 ORDER BY t1.a, t2.a;
-                          QUERY PLAN                           
----------------------------------------------------------------
+                               QUERY PLAN                                
+-------------------------------------------------------------------------
  Sort
    Sort Key: t1.a, t2.a
-   ->  Hash Full Join
-         Hash Cond: ((t2.c)::text = (t1.c)::text)
-         Filter: ((COALESCE(t1.b, 0) + COALESCE(t2.b, 0)) = 0)
-         ->  Append
+   ->  Append
+         ->  Hash Full Join
+               Hash Cond: ((t2.c)::text = (t1.c)::text)
+               Filter: ((COALESCE(t1.b, 0) + COALESCE(t2.b, 0)) = 0)
                ->  Seq Scan on plt2_p4 t2
-               ->  Seq Scan on plt2_p1 t2_1
-               ->  Seq Scan on plt2_p2 t2_2
-               ->  Seq Scan on plt2_p3 t2_3
-         ->  Hash
-               ->  Append
+               ->  Hash
                      ->  Seq Scan on plt1_p4 t1
+         ->  Hash Full Join
+               Hash Cond: ((t2_1.c)::text = (t1_1.c)::text)
+               Filter: ((COALESCE(t1_1.b, 0) + COALESCE(t2_1.b, 0)) = 0)
+               ->  Seq Scan on plt2_p1 t2_1
+               ->  Hash
                      ->  Seq Scan on plt1_p1 t1_1
-                     ->  Seq Scan on plt1_p2 t1_2
-                     ->  Seq Scan on plt1_p3 t1_3
-(16 rows)
+         ->  Hash Full Join
+               Hash Cond: ((t1_2.c)::text = (t2_2.c)::text)
+               Filter: ((COALESCE(t1_2.b, 0) + COALESCE(t2_2.b, 0)) = 0)
+               ->  Seq Scan on plt1_p2 t1_2
+               ->  Hash
+                     ->  Seq Scan on plt2_p2 t2_2
+         ->  Hash Full Join
+               Hash Cond: ((t1_3.c)::text = (t2_3.c)::text)
+               Filter: ((COALESCE(t1_3.b, 0) + COALESCE(t2_3.b, 0)) = 0)
+               ->  Seq Scan on plt1_p3 t1_3
+               ->  Hash
+                     ->  Seq Scan on plt2_p3 t2_3
+(27 rows)
 
 -- semi join
 EXPLAIN (COSTS OFF)
@@ -3973,27 +4014,34 @@ select t1.a, t1.b, t1.c from plt1 t1 where exists (select 1 from plt2 t2 WHERE t
 --------------------------------------------------------------
  Sort
    Sort Key: t1.a, t1.c
-   ->  Hash Join
-         Hash Cond: ((t1.c)::text = (t2.c)::text)
-         ->  Append
-               ->  Seq Scan on plt1_p4 t1
-                     Filter: (b = 0)
-               ->  Seq Scan on plt1_p1 t1_1
-                     Filter: (b = 0)
+   ->  Append
+         ->  Nested Loop
+               Join Filter: ((t1.c)::text = (t2.c)::text)
+               ->  HashAggregate
+                     Group Key: (t2.c)::text
+                     ->  Seq Scan on plt2_p4 t2
+               ->  Materialize
+                     ->  Seq Scan on plt1_p4 t1
+                           Filter: (b = 0)
+         ->  Nested Loop
+               Join Filter: ((t1_1.c)::text = (t2_1.c)::text)
+               ->  HashAggregate
+                     Group Key: (t2_1.c)::text
+                     ->  Seq Scan on plt2_p1 t2_1
+               ->  Materialize
+                     ->  Seq Scan on plt1_p1 t1_1
+                           Filter: (b = 0)
+         ->  Nested Loop Semi Join
+               Join Filter: ((t1_2.c)::text = (t2_2.c)::text)
                ->  Seq Scan on plt1_p2 t1_2
                      Filter: (b = 0)
+               ->  Seq Scan on plt2_p2 t2_2
+         ->  Nested Loop Semi Join
+               Join Filter: ((t1_3.c)::text = (t2_3.c)::text)
                ->  Seq Scan on plt1_p3 t1_3
                      Filter: (b = 0)
-         ->  Hash
-               ->  HashAggregate
-                     Group Key: (t2.c)::text
-                     ->  Result
-                           ->  Append
-                                 ->  Seq Scan on plt2_p4 t2
-                                 ->  Seq Scan on plt2_p1 t2_1
-                                 ->  Seq Scan on plt2_p2 t2_2
-                                 ->  Seq Scan on plt2_p3 t2_3
-(22 rows)
+               ->  Seq Scan on plt2_p3 t2_3
+(29 rows)
 
 EXPLAIN (COSTS OFF)
 select t1.a, t1.b, t1.c from plt2 t1 where exists (select 1 from plt1 t2 WHERE t1.c = t2.c) and t1.b = 0 order by t1.a, t1.b, t1.c;
@@ -4001,78 +4049,92 @@ select t1.a, t1.b, t1.c from plt2 t1 where exists (select 1 from plt1 t2 WHERE t
 --------------------------------------------------------------
  Sort
    Sort Key: t1.a, t1.c
-   ->  Hash Join
-         Hash Cond: ((t1.c)::text = (t2.c)::text)
-         ->  Append
-               ->  Seq Scan on plt2_p4 t1
-                     Filter: (b = 0)
+   ->  Append
+         ->  Nested Loop
+               Join Filter: ((t1.c)::text = (t2.c)::text)
+               ->  HashAggregate
+                     Group Key: (t2.c)::text
+                     ->  Seq Scan on plt1_p4 t2
+               ->  Materialize
+                     ->  Seq Scan on plt2_p4 t1
+                           Filter: (b = 0)
+         ->  Nested Loop Semi Join
+               Join Filter: ((t1_1.c)::text = (t2_1.c)::text)
                ->  Seq Scan on plt2_p1 t1_1
                      Filter: (b = 0)
+               ->  Seq Scan on plt1_p1 t2_1
+         ->  Nested Loop Semi Join
+               Join Filter: ((t1_2.c)::text = (t2_2.c)::text)
                ->  Seq Scan on plt2_p2 t1_2
                      Filter: (b = 0)
+               ->  Seq Scan on plt1_p2 t2_2
+         ->  Nested Loop Semi Join
+               Join Filter: ((t1_3.c)::text = (t2_3.c)::text)
                ->  Seq Scan on plt2_p3 t1_3
                      Filter: (b = 0)
-         ->  Hash
-               ->  HashAggregate
-                     Group Key: (t2.c)::text
-                     ->  Result
-                           ->  Append
-                                 ->  Seq Scan on plt1_p4 t2
-                                 ->  Seq Scan on plt1_p1 t2_1
-                                 ->  Seq Scan on plt1_p2 t2_2
-                                 ->  Seq Scan on plt1_p3 t2_3
-(22 rows)
+               ->  Seq Scan on plt1_p3 t2_3
+(26 rows)
 
 -- anti join
 EXPLAIN (COSTS OFF)
 select t1.a, t1.b, t1.c from plt1 t1 where not exists (select 1 from plt2 t2 WHERE t1.c = t2.c) and t1.b = 0 order by t1.a, t1.b, t1.c;
-                    QUERY PLAN                    
---------------------------------------------------
+                          QUERY PLAN                          
+--------------------------------------------------------------
  Sort
    Sort Key: t1.a, t1.c
-   ->  Hash Anti Join
-         Hash Cond: ((t1.c)::text = (t2.c)::text)
-         ->  Append
+   ->  Append
+         ->  Nested Loop Anti Join
+               Join Filter: ((t1.c)::text = (t2.c)::text)
                ->  Seq Scan on plt1_p4 t1
                      Filter: (b = 0)
+               ->  Seq Scan on plt2_p4 t2
+         ->  Hash Anti Join
+               Hash Cond: ((t1_1.c)::text = (t2_1.c)::text)
                ->  Seq Scan on plt1_p1 t1_1
                      Filter: (b = 0)
+               ->  Hash
+                     ->  Seq Scan on plt2_p1 t2_1
+         ->  Nested Loop Anti Join
+               Join Filter: ((t1_2.c)::text = (t2_2.c)::text)
                ->  Seq Scan on plt1_p2 t1_2
                      Filter: (b = 0)
+               ->  Seq Scan on plt2_p2 t2_2
+         ->  Nested Loop Anti Join
+               Join Filter: ((t1_3.c)::text = (t2_3.c)::text)
                ->  Seq Scan on plt1_p3 t1_3
                      Filter: (b = 0)
-         ->  Hash
-               ->  Append
-                     ->  Seq Scan on plt2_p4 t2
-                     ->  Seq Scan on plt2_p1 t2_1
-                     ->  Seq Scan on plt2_p2 t2_2
-                     ->  Seq Scan on plt2_p3 t2_3
-(19 rows)
+               ->  Seq Scan on plt2_p3 t2_3
+(24 rows)
 
 EXPLAIN (COSTS OFF)
 select t1.a, t1.b, t1.c from plt2 t1 where not exists (select 1 from plt1 t2 WHERE t1.c = t2.c) and t1.b = 0 order by t1.a, t1.b, t1.c;
-                    QUERY PLAN                    
---------------------------------------------------
+                          QUERY PLAN                          
+--------------------------------------------------------------
  Sort
    Sort Key: t1.a, t1.c
-   ->  Hash Anti Join
-         Hash Cond: ((t1.c)::text = (t2.c)::text)
-         ->  Append
+   ->  Append
+         ->  Hash Anti Join
+               Hash Cond: ((t1.c)::text = (t2.c)::text)
                ->  Seq Scan on plt2_p4 t1
                      Filter: (b = 0)
+               ->  Hash
+                     ->  Seq Scan on plt1_p4 t2
+         ->  Nested Loop Anti Join
+               Join Filter: ((t1_1.c)::text = (t2_1.c)::text)
                ->  Seq Scan on plt2_p1 t1_1
                      Filter: (b = 0)
+               ->  Seq Scan on plt1_p1 t2_1
+         ->  Nested Loop Anti Join
+               Join Filter: ((t1_2.c)::text = (t2_2.c)::text)
                ->  Seq Scan on plt2_p2 t1_2
                      Filter: (b = 0)
+               ->  Seq Scan on plt1_p2 t2_2
+         ->  Nested Loop Anti Join
+               Join Filter: ((t1_3.c)::text = (t2_3.c)::text)
                ->  Seq Scan on plt2_p3 t1_3
                      Filter: (b = 0)
-         ->  Hash
-               ->  Append
-                     ->  Seq Scan on plt1_p4 t2
-                     ->  Seq Scan on plt1_p1 t2_1
-                     ->  Seq Scan on plt1_p2 t2_2
-                     ->  Seq Scan on plt1_p3 t2_3
-(19 rows)
+               ->  Seq Scan on plt1_p3 t2_3
+(24 rows)
 
 -- joins where one of the relations is proven empty
 EXPLAIN (COSTS OFF)
diff --git a/src/test/regress/sql/partition_join.sql b/src/test/regress/sql/partition_join.sql
index d8434f6b1ad..a552874742f 100644
--- a/src/test/regress/sql/partition_join.sql
+++ b/src/test/regress/sql/partition_join.sql
@@ -561,10 +561,7 @@ EXPLAIN (COSTS OFF)
 select t1.a, t1.b, t1.c from plt2 t1 where not exists (select 1 from plt1 t2 WHERE t1.c = t2.c) and t1.b = 0 order by t1.a, t1.b, t1.c;
 select t1.a, t1.b, t1.c from plt2 t1 where not exists (select 1 from plt1 t2 WHERE t1.c = t2.c) and t1.b = 0 order by t1.a, t1.b, t1.c;
 
--- partition have a NULL on both side with different partition bounds w.r.t other side
--- NULL when NULL comparision is not strict i.e. NULL=NULL allowed
--- Partition-wise join can not handle the case when one partition from one side
--- matches with multiple partitions on the other side
+-- test the null-partition handling in the new partition-matching algorithm
 DROP TABLE plt1_p3;
 CREATE TABLE plt1_p3 PARTITION OF plt1 FOR VALUES IN (NULL,'0008','0009');
 INSERT INTO plt1 SELECT i, i % :cond_mod, case when i % :part_mod = 7 then NULL else to_char(i % :part_mod, 'FM0000') end FROM generate_series(0, :num_rows) i WHERE i % :part_mod IN (7,8,9);
-- 
2.18.0