2 files changed, 19 insertions, 0 deletions
diff --git a/src/test/regress/expected/incremental_sort.out b/src/test/regress/expected/incremental_sort.out
index d5745838440..68ca321163b 100644
--- a/src/test/regress/expected/incremental_sort.out
+++ b/src/test/regress/expected/incremental_sort.out
@@ -676,6 +676,21 @@ select * from (select * from t order by a) s order by a, b limit 70;
 (70 rows)
 
 -- Checks case where we hit a group boundary at the last tuple of a batch.
+-- Because the full sort state is bounded, we scan 64 tuples (the mode
+-- transition point) but only retain 5. Thus when we transition modes, all
+-- tuples in the full sort state have different prefix keys.
+explain (costs off) select * from (select * from t order by a) s order by a, b limit 5;
+           QUERY PLAN            
+---------------------------------
+ Limit
+   ->  Incremental Sort
+         Sort Key: t.a, t.b
+         Presorted Key: t.a
+         ->  Sort
+               Sort Key: t.a
+               ->  Seq Scan on t
+(7 rows)
+
 select * from (select * from t order by a) s order by a, b limit 5;
  a | b 
 ---+---
diff --git a/src/test/regress/sql/incremental_sort.sql b/src/test/regress/sql/incremental_sort.sql
index 9965fcd7776..81429164d45 100644
--- a/src/test/regress/sql/incremental_sort.sql
+++ b/src/test/regress/sql/incremental_sort.sql
@@ -150,6 +150,10 @@ analyze t;
 explain (costs off) select * from (select * from t order by a) s order by a, b limit 70;
 select * from (select * from t order by a) s order by a, b limit 70;
 -- Checks case where we hit a group boundary at the last tuple of a batch.
+-- Because the full sort state is bounded, we scan 64 tuples (the mode
+-- transition point) but only retain 5. Thus when we transition modes, all
+-- tuples in the full sort state have different prefix keys.
+explain (costs off) select * from (select * from t order by a) s order by a, b limit 5;
 select * from (select * from t order by a) s order by a, b limit 5;
 
 -- Test rescan.