3 files changed, 57 insertions, 2 deletions
diff --git a/src/backend/executor/nodeHash.c b/src/backend/executor/nodeHash.c
index 47160e4aa07..9ed09a7b0ca 100644
--- a/src/backend/executor/nodeHash.c
+++ b/src/backend/executor/nodeHash.c
@@ -1575,8 +1575,19 @@ ExecHashRemoveNextSkewBucket(HashJoinTable hashtable)
 		if (batchno == hashtable->curbatch)
 		{
 			/* Move the tuple to the main hash table */
-			hashTuple->next = hashtable->buckets[bucketno];
-			hashtable->buckets[bucketno] = hashTuple;
+			HashJoinTuple copyTuple;
+
+			/*
+			 * We must copy the tuple into the dense storage, else it will not
+			 * be found by, eg, ExecHashIncreaseNumBatches.
+			 */
+			copyTuple = (HashJoinTuple) dense_alloc(hashtable, tupleSize);
+			memcpy(copyTuple, hashTuple, tupleSize);
+			pfree(hashTuple);
+
+			copyTuple->next = hashtable->buckets[bucketno];
+			hashtable->buckets[bucketno] = copyTuple;
+
 			/* We have reduced skew space, but overall space doesn't change */
 			hashtable->spaceUsedSkew -= tupleSize;
 		}
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 64f046ee0bb..0ac21bb813e 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -2331,6 +2331,34 @@ select tt1.*, tt2.* from tt2 right join tt1 on tt1.joincol = tt2.joincol;
 reset enable_hashjoin;
 reset enable_nestloop;
 --
+-- regression test for bug #13908 (hash join with skew tuples & nbatch increase)
+--
+set work_mem to '64kB';
+set enable_mergejoin to off;
+explain (costs off)
+select count(*) from tenk1 a, tenk1 b
+  where a.hundred = b.thousand and (b.fivethous % 10) < 10;
+                         QUERY PLAN                         
+------------------------------------------------------------
+ Aggregate
+   ->  Hash Join
+         Hash Cond: (a.hundred = b.thousand)
+         ->  Index Only Scan using tenk1_hundred on tenk1 a
+         ->  Hash
+               ->  Seq Scan on tenk1 b
+                     Filter: ((fivethous % 10) < 10)
+(7 rows)
+
+select count(*) from tenk1 a, tenk1 b
+  where a.hundred = b.thousand and (b.fivethous % 10) < 10;
+ count  
+--------
+ 100000
+(1 row)
+
+reset work_mem;
+reset enable_mergejoin;
+--
 -- regression test for 8.2 bug with improper re-ordering of left joins
 --
 create temp table tt3(f1 int, f2 text);
diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index 0358d00e404..fafbb3fb003 100644
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -464,6 +464,22 @@ reset enable_hashjoin;
 reset enable_nestloop;
 
 --
+-- regression test for bug #13908 (hash join with skew tuples & nbatch increase)
+--
+
+set work_mem to '64kB';
+set enable_mergejoin to off;
+
+explain (costs off)
+select count(*) from tenk1 a, tenk1 b
+  where a.hundred = b.thousand and (b.fivethous % 10) < 10;
+select count(*) from tenk1 a, tenk1 b
+  where a.hundred = b.thousand and (b.fivethous % 10) < 10;
+
+reset work_mem;
+reset enable_mergejoin;
+
+--
 -- regression test for 8.2 bug with improper re-ordering of left joins
 --