Fix incorrect row count in EXPLAIN ANALYZE INSERT .. ON CONFLICT output

INSERT ... ON CONFLICT statements record few metrics in the ModifyTable
node's instrument but they get overwritten by hypertable_modify_explain
causing wrong output in EXPLAIN ANALYZE statments. Fix it by saving the
metrics into HypertableModify node before replacing them.

Fixes #6014

(cherry picked from commit 8e941b8)

.unreleased/bugfix_6015

@@ -0,0 +1 @@
+Fixes: #6015 Correct row count in EXPLAIN ANALYZE INSERT .. ON CONFLICT output

src/nodes/hypertable_modify.c

@@ -212,9 +212,18 @@ hypertable_modify_explain(CustomScanState *node, List *ancestors, ExplainState *
 	}
 
 	/*
-	 * Since we hijack the ModifyTable node instrumentation on ModifyTable will
+	 * Since we hijack the ModifyTable node, instrumentation on ModifyTable will
 	 * be missing so we set it to instrumentation of HypertableModify node.
 	 */
+	if (mtstate->ps.instrument)
+	{
+		/*
+		 * INSERT .. ON CONFLICT statements record few metrics in the ModifyTable node.
+		 * So, copy them into HypertableModify node before replacing them.
+		 */
+		node->ss.ps.instrument->ntuples2 = mtstate->ps.instrument->ntuples2;
+		node->ss.ps.instrument->nfiltered1 = mtstate->ps.instrument->nfiltered1;
+	}
 	mtstate->ps.instrument = node->ss.ps.instrument;
 #endif
 

test/expected/upsert.out

@@ -29,6 +29,25 @@ SELECT * FROM upsert_test;
  Fri Jan 20 09:00:01 2017 | 23.8 | yellow
 (1 row)
 
+-- Test 'Tuples Inserted' and 'Conflicting Tuples' values in EXPLAIN ANALYZE
+EXPLAIN (VERBOSE, ANALYZE, COSTS FALSE, TIMING FALSE, SUMMARY FALSE)
+  INSERT INTO upsert_test VALUES
+    ('2017-01-20T09:00:01', 28.5, 'blue'),
+    ('2017-01-20T09:00:01', 21.9, 'red'),
+    ('2017-01-20T10:00:01', 2.4, 'pink') ON CONFLICT DO NOTHING;
+                                       QUERY PLAN                                       
+----------------------------------------------------------------------------------------
+ Custom Scan (HypertableModify) (actual rows=0 loops=1)
+   ->  Insert on public.upsert_test (actual rows=0 loops=1)
+         Conflict Resolution: NOTHING
+         Tuples Inserted: 1
+         Conflicting Tuples: 2
+         ->  Custom Scan (ChunkDispatch) (actual rows=3 loops=1)
+               Output: "*VALUES*".column1, "*VALUES*".column2, "*VALUES*".column3
+               ->  Values Scan on "*VALUES*" (actual rows=3 loops=1)
+                     Output: "*VALUES*".column1, "*VALUES*".column2, "*VALUES*".column3
+(9 rows)
+
 -- Test ON CONFLICT ON CONSTRAINT
 INSERT INTO upsert_test VALUES ('2017-01-20T09:00:01', 12.3, 'yellow') ON CONFLICT ON CONSTRAINT upsert_test_pkey
 DO UPDATE SET temp = 12.3 RETURNING time, temp, color;

test/sql/upsert.sql

@@ -10,6 +10,13 @@ DO UPDATE SET temp = 23.8 RETURNING *;
 INSERT INTO upsert_test VALUES ('2017-01-20T09:00:01', 78.4, 'yellow') ON CONFLICT DO NOTHING;
 SELECT * FROM upsert_test;
 
+-- Test 'Tuples Inserted' and 'Conflicting Tuples' values in EXPLAIN ANALYZE
+EXPLAIN (VERBOSE, ANALYZE, COSTS FALSE, TIMING FALSE, SUMMARY FALSE)
+  INSERT INTO upsert_test VALUES
+    ('2017-01-20T09:00:01', 28.5, 'blue'),
+    ('2017-01-20T09:00:01', 21.9, 'red'),
+    ('2017-01-20T10:00:01', 2.4, 'pink') ON CONFLICT DO NOTHING;
+
 -- Test ON CONFLICT ON CONSTRAINT
 INSERT INTO upsert_test VALUES ('2017-01-20T09:00:01', 12.3, 'yellow') ON CONFLICT ON CONSTRAINT upsert_test_pkey
 DO UPDATE SET temp = 12.3 RETURNING time, temp, color;