2 files changed, 104 insertions, 0 deletions
diff --git a/src/test/regress/expected/select_distinct.out b/src/test/regress/expected/select_distinct.out
index 11c6f50fbfa..0c8e10f88a5 100644
--- a/src/test/regress/expected/select_distinct.out
+++ b/src/test/regress/expected/select_distinct.out
@@ -210,6 +210,73 @@ DROP TABLE distinct_hash_1;
 DROP TABLE distinct_hash_2;
 DROP TABLE distinct_group_1;
 DROP TABLE distinct_group_2;
+-- Test parallel DISTINCT
+SET parallel_tuple_cost=0;
+SET parallel_setup_cost=0;
+SET min_parallel_table_scan_size=0;
+-- Ensure we get a parallel plan
+EXPLAIN (costs off)
+SELECT DISTINCT four FROM tenk1;
+                     QUERY PLAN                     
+----------------------------------------------------
+ Unique
+   ->  Sort
+         Sort Key: four
+         ->  Gather
+               Workers Planned: 2
+               ->  HashAggregate
+                     Group Key: four
+                     ->  Parallel Seq Scan on tenk1
+(8 rows)
+
+-- Ensure the parallel plan produces the correct results
+SELECT DISTINCT four FROM tenk1;
+ four 
+------
+    0
+    1
+    2
+    3
+(4 rows)
+
+CREATE OR REPLACE FUNCTION distinct_func(a INT) RETURNS INT AS $$
+  BEGIN
+    RETURN a;
+  END;
+$$ LANGUAGE plpgsql PARALLEL UNSAFE;
+-- Ensure we don't do parallel distinct with a parallel unsafe function
+EXPLAIN (COSTS OFF)
+SELECT DISTINCT distinct_func(1) FROM tenk1;
+                        QUERY PLAN                        
+----------------------------------------------------------
+ Unique
+   ->  Sort
+         Sort Key: (distinct_func(1))
+         ->  Index Only Scan using tenk1_hundred on tenk1
+(4 rows)
+
+-- make the function parallel safe
+CREATE OR REPLACE FUNCTION distinct_func(a INT) RETURNS INT AS $$
+  BEGIN
+    RETURN a;
+  END;
+$$ LANGUAGE plpgsql PARALLEL SAFE;
+-- Ensure we do parallel distinct now that the function is parallel safe
+EXPLAIN (COSTS OFF)
+SELECT DISTINCT distinct_func(1) FROM tenk1;
+                  QUERY PLAN                  
+----------------------------------------------
+ Unique
+   ->  Sort
+         Sort Key: (distinct_func(1))
+         ->  Gather
+               Workers Planned: 2
+               ->  Parallel Seq Scan on tenk1
+(6 rows)
+
+RESET min_parallel_table_scan_size;
+RESET parallel_setup_cost;
+RESET parallel_tuple_cost;
 --
 -- Also, some tests of IS DISTINCT FROM, which doesn't quite deserve its
 -- very own regression file.
diff --git a/src/test/regress/sql/select_distinct.sql b/src/test/regress/sql/select_distinct.sql
index 33102744ebf..e00582e46c1 100644
--- a/src/test/regress/sql/select_distinct.sql
+++ b/src/test/regress/sql/select_distinct.sql
@@ -107,6 +107,43 @@ DROP TABLE distinct_hash_2;
 DROP TABLE distinct_group_1;
 DROP TABLE distinct_group_2;
 
+-- Test parallel DISTINCT
+SET parallel_tuple_cost=0;
+SET parallel_setup_cost=0;
+SET min_parallel_table_scan_size=0;
+
+-- Ensure we get a parallel plan
+EXPLAIN (costs off)
+SELECT DISTINCT four FROM tenk1;
+
+-- Ensure the parallel plan produces the correct results
+SELECT DISTINCT four FROM tenk1;
+
+CREATE OR REPLACE FUNCTION distinct_func(a INT) RETURNS INT AS $$
+  BEGIN
+    RETURN a;
+  END;
+$$ LANGUAGE plpgsql PARALLEL UNSAFE;
+
+-- Ensure we don't do parallel distinct with a parallel unsafe function
+EXPLAIN (COSTS OFF)
+SELECT DISTINCT distinct_func(1) FROM tenk1;
+
+-- make the function parallel safe
+CREATE OR REPLACE FUNCTION distinct_func(a INT) RETURNS INT AS $$
+  BEGIN
+    RETURN a;
+  END;
+$$ LANGUAGE plpgsql PARALLEL SAFE;
+
+-- Ensure we do parallel distinct now that the function is parallel safe
+EXPLAIN (COSTS OFF)
+SELECT DISTINCT distinct_func(1) FROM tenk1;
+
+RESET min_parallel_table_scan_size;
+RESET parallel_setup_cost;
+RESET parallel_tuple_cost;
+
 --
 -- Also, some tests of IS DISTINCT FROM, which doesn't quite deserve its
 -- very own regression file.