index 01fa45b9255150153dd7ac8782f78f3ee36c3c0f..342f5ad8d0a11f6d00a49e7b8c2a1c2cdafcc987 100644 (file)
@@ -4737,11 +4737,45 @@ create_partial_distinct_paths(PlannerInfo *root, RelOptInfo *input_rel,
-1.0);
}
- add_partial_path(partial_distinct_rel, (Path *)
- create_upper_unique_path(root, partial_distinct_rel,
- sorted_path,
- list_length(root->distinct_pathkeys),
- numDistinctRows));
+ /*
+ * An empty distinct_pathkeys means all tuples have the same value
+ * for the DISTINCT clause. See create_final_distinct_paths()
+ */
+ if (root->distinct_pathkeys == NIL)
+ {
+ Node *limitCount;
+
+ limitCount = (Node *) makeConst(INT8OID, -1, InvalidOid,
+ sizeof(int64),
+ Int64GetDatum(1), false,
+ FLOAT8PASSBYVAL);
+
+ /*
+ * Apply a LimitPath onto the partial path to restrict the
+ * tuples from each worker to 1. create_final_distinct_paths
+ * will need to apply an additional LimitPath to restrict this
+ * to a single row after the Gather node. If the query
+ * already has a LIMIT clause, then we could end up with three
+ * Limit nodes in the final plan. Consolidating the top two
+ * of these could be done, but does not seem worth troubling
+ * over.
+ */
+ add_partial_path(partial_distinct_rel, (Path *)
+ create_limit_path(root, partial_distinct_rel,
+ sorted_path,
+ NULL,
+ limitCount,
+ LIMIT_OPTION_COUNT,
+ 0, 1));
+ }
+ else
+ {
+ add_partial_path(partial_distinct_rel, (Path *)
+ create_upper_unique_path(root, partial_distinct_rel,
+ sorted_path,
+ list_length(root->distinct_pathkeys),
+ numDistinctRows));
+ }
}
}
index 9d44ea8056d1949b66bd591ac2633f3d4e9e75f1..1f72756ccb4c60e0873da354966a792097acb12e 100644 (file)
@@ -348,6 +348,26 @@ SELECT DISTINCT four,1,2,3 FROM tenk1 WHERE four = 0;
0 | 1 | 2 | 3
(1 row)
+SET parallel_setup_cost=0;
+SET min_parallel_table_scan_size=0;
+SET max_parallel_workers_per_gather=2;
+-- Ensure we get a plan with a Limit 1 in both partial distinct and final
+-- distinct
+EXPLAIN (COSTS OFF)
+SELECT DISTINCT four FROM tenk1 WHERE four = 10;
+ QUERY PLAN
+----------------------------------------------
+ Limit
+ -> Gather
+ Workers Planned: 2
+ -> Limit
+ -> Parallel Seq Scan on tenk1
+ Filter: (four = 10)
+(6 rows)
+
+RESET max_parallel_workers_per_gather;
+RESET min_parallel_table_scan_size;
+RESET parallel_setup_cost;
--
-- Also, some tests of IS DISTINCT FROM, which doesn't quite deserve its
-- very own regression file.
index 1643526d991807b38c7d651d3a4390a784f02edb..da92c197aba5c9102ef57ec3f47045593526820c 100644 (file)
@@ -180,6 +180,19 @@ SELECT DISTINCT four,1,2,3 FROM tenk1 WHERE four = 0;
-- Ensure we only get 1 row
SELECT DISTINCT four,1,2,3 FROM tenk1 WHERE four = 0;
+SET parallel_setup_cost=0;
+SET min_parallel_table_scan_size=0;
+SET max_parallel_workers_per_gather=2;
+
+-- Ensure we get a plan with a Limit 1 in both partial distinct and final
+-- distinct
+EXPLAIN (COSTS OFF)
+SELECT DISTINCT four FROM tenk1 WHERE four = 10;
+
+RESET max_parallel_workers_per_gather;
+RESET min_parallel_table_scan_size;
+RESET parallel_setup_cost;
+
--
-- Also, some tests of IS DISTINCT FROM, which doesn't quite deserve its
-- very own regression file.