diff --git a/src/backend/statistics/mvdistinct.c b/src/backend/statistics/mvdistinct.c
index 4b4ecec9361..bf63f2b9a73 100644
--- a/src/backend/statistics/mvdistinct.c
+++ b/src/backend/statistics/mvdistinct.c
@@ -33,6 +33,7 @@
 #include "statistics/statistics.h"
 #include "utils/fmgrprotos.h"
 #include "utils/lsyscache.h"
+#include "utils/memutils.h"
 #include "utils/syscache.h"
 #include "utils/typcache.h"
 
@@ -93,6 +94,7 @@ statext_ndistinct_build(double totalrows, StatsBuildData *data)
 	int			itemcnt;
 	int			numattrs = data->nattnums;
 	int			numcombs = num_combinations(numattrs);
+	MemoryContext cxt;
 
 	result = palloc(offsetof(MVNDistinct, items) +
 					numcombs * sizeof(MVNDistinctItem));
@@ -100,6 +102,10 @@ statext_ndistinct_build(double totalrows, StatsBuildData *data)
 	result->type = STATS_NDISTINCT_TYPE_BASIC;
 	result->nitems = numcombs;
 
+	cxt = AllocSetContextCreate(CurrentMemoryContext,
+								"ndistinct_for_combination cxt",
+								ALLOCSET_DEFAULT_SIZES);
+
 	itemcnt = 0;
 	for (k = 2; k <= numattrs; k++)
 	{
@@ -113,6 +119,7 @@ statext_ndistinct_build(double totalrows, StatsBuildData *data)
 		{
 			MVNDistinctItem *item = &result->items[itemcnt];
 			int			j;
+			MemoryContext oldcxt;
 
 			item->attributes = palloc(sizeof(AttrNumber) * k);
 			item->nattributes = k;
@@ -125,8 +132,12 @@ statext_ndistinct_build(double totalrows, StatsBuildData *data)
 				Assert(AttributeNumberIsValid(item->attributes[j]));
 			}
 
+			/* release memory used by ndistinct calculation */
+			oldcxt = MemoryContextSwitchTo(cxt);
 			item->ndistinct =
 				ndistinct_for_combination(totalrows, data, k, combination);
+			MemoryContextSwitchTo(oldcxt);
+			MemoryContextReset(cxt);
 
 			itemcnt++;
 			Assert(itemcnt <= result->nitems);
@@ -135,6 +146,8 @@ statext_ndistinct_build(double totalrows, StatsBuildData *data)
 		generator_free(generator);
 	}
 
+	MemoryContextDelete(cxt);
+
 	/* must consume exactly the whole output array */
 	Assert(itemcnt == result->nitems);