diff --git a/executor/union_scan.go b/executor/union_scan.go
index e08e90249375c..160c921bd8ed7 100644
--- a/executor/union_scan.go
+++ b/executor/union_scan.go
@@ -112,7 +112,11 @@ func (us *UnionScanExec) open(ctx context.Context) error {
 func (us *UnionScanExec) Next(ctx context.Context, req *chunk.Chunk) error {
 	us.memBuf.RLock()
 	defer us.memBuf.RUnlock()
+
+	// Assume req.Capacity() > 0 after GrowAndReset(), if this assumption fail,
+	// the for-loop may exit without read one single row!
 	req.GrowAndReset(us.maxChunkSize)
+
 	mutableRow := chunk.MutRowFromTypes(retTypes(us))
 	for i, batchSize := 0, req.Capacity(); i < batchSize; i++ {
 		row, err := us.getOneRow(ctx)
diff --git a/executor/union_scan_test.go b/executor/union_scan_test.go
index 5e0727458230e..fca4e2aa8d9da 100644
--- a/executor/union_scan_test.go
+++ b/executor/union_scan_test.go
@@ -403,3 +403,170 @@ func (s *testSuite7) TestForApplyAndUnionScan(c *C) {
 	tk.MustQuery("select c_int, c_str from t where (select count(*) from t1 where t1.c_int in (t.c_int, t.c_int + 2, t.c_int + 10)) > 2").Check(testkit.Rows())
 	tk.MustExec("rollback")
 }
+<<<<<<< HEAD
+=======
+
+func TestIssue28073(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t1, t2")
+	tk.MustExec("create table t1 (c_int int, c_str varchar(40), primary key (c_int, c_str) , key(c_int)) partition by hash (c_int) partitions 4")
+	tk.MustExec("create table t2 like t1")
+	tk.MustExec("insert into t1 values (1, 'flamboyant mcclintock')")
+	tk.MustExec("insert into t2 select * from t1")
+
+	tk.MustExec("begin")
+	tk.MustExec("insert into t2 (c_int, c_str) values (2, 'romantic grothendieck')")
+	tk.MustQuery("select * from t2 left join t1 on t1.c_int = t2.c_int for update").Sort().Check(
+		testkit.Rows(
+			"1 flamboyant mcclintock 1 flamboyant mcclintock",
+			"2 romantic grothendieck <nil> <nil>",
+		))
+	tk.MustExec("commit")
+
+	// Check no key is written to table ID 0
+	txn, err := store.Begin()
+	require.NoError(t, err)
+	start := tablecodec.EncodeTablePrefix(0)
+	end := tablecodec.EncodeTablePrefix(1)
+	iter, err := txn.Iter(start, end)
+	require.NoError(t, err)
+
+	exist := false
+	for iter.Valid() {
+		require.Nil(t, iter.Next())
+		exist = true
+		break
+	}
+	require.False(t, exist)
+
+	// Another case, left join on partition table should not generate locks on physical ID = 0
+	tk.MustExec("drop table if exists t1, t2;")
+	tk.MustExec("create table t1  (c_int int, c_str varchar(40), primary key (c_int, c_str));")
+	tk.MustExec("create table t2  (c_int int, c_str varchar(40), primary key (c_int)) partition by hash (c_int) partitions 4;")
+	tk.MustExec("insert into t1 (`c_int`, `c_str`) values (1, 'upbeat solomon'), (5, 'sharp rubin');")
+	tk.MustExec("insert into t2 (`c_int`, `c_str`) values (1, 'clever haibt'), (4, 'kind margulis');")
+	tk.MustExec("begin pessimistic;")
+	tk.MustQuery("select * from t1 left join t2 on t1.c_int = t2.c_int for update;").Check(testkit.Rows(
+		"1 upbeat solomon 1 clever haibt",
+		"5 sharp rubin <nil> <nil>",
+	))
+	key, err := hex.DecodeString("7480000000000000005F728000000000000000")
+	require.NoError(t, err)
+	h := helper.NewHelper(store.(helper.Storage))
+	resp, err := h.GetMvccByEncodedKey(key)
+	require.NoError(t, err)
+	require.Nil(t, resp.Info.Lock)
+	require.Len(t, resp.Info.Writes, 0)
+	require.Len(t, resp.Info.Values, 0)
+
+	tk.MustExec("rollback;")
+}
+
+func TestIssue32422(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+
+	tk.MustExec("create table t (id int, c int, index(id));")
+	tk.MustExec("insert into t values (3,3), (4,4), (5,5);")
+	tk.MustExec("alter table t cache;")
+
+	var cacheUsed bool
+	for i := 0; i < 20; i++ {
+		tk.MustQuery("select id+1, c from t where c = 4;").Check(testkit.Rows("5 4"))
+		if tk.Session().GetSessionVars().StmtCtx.ReadFromTableCache {
+			cacheUsed = true
+			break
+		}
+		time.Sleep(50 * time.Millisecond)
+	}
+	require.True(t, cacheUsed)
+
+	tk.MustQuery("select id+1, c from t where c = 4;").Check(testkit.Rows("5 4"))
+
+	// Some extra tests.
+	// Since cached table use UnionScanExec utilities, check what happens when they work together.
+	// In these cases, the cache data serve as the snapshot, tikv is skipped, and txn membuffer works the same way.
+	tk.MustExec("begin")
+	tk.MustQuery("select id+1, c from t where c = 4;").Check(testkit.Rows("5 4"))
+	tk.MustExec("insert into t values (6, 6)")
+	// Check for the new added data.
+	tk.HasPlan("select id+1, c from t where c = 6;", "UnionScan")
+	tk.MustQuery("select id+1, c from t where c = 6;").Check(testkit.Rows("7 6"))
+	require.True(t, tk.Session().GetSessionVars().StmtCtx.ReadFromTableCache)
+	// Check for the old data.
+	tk.MustQuery("select id+1, c from t where c = 4;").Check(testkit.Rows("5 4"))
+	require.True(t, tk.Session().GetSessionVars().StmtCtx.ReadFromTableCache)
+
+	// Point get
+	tk.HasPlan("select id+1, c from t where id = 6", "PointGet")
+	tk.MustQuery("select id+1, c from t where id = 6").Check(testkit.Rows("7 6"))
+	require.True(t, tk.Session().GetSessionVars().StmtCtx.ReadFromTableCache)
+	tk.MustQuery("select id+1, c from t where id = 4").Check(testkit.Rows("5 4"))
+	require.True(t, tk.Session().GetSessionVars().StmtCtx.ReadFromTableCache)
+
+	// Index Lookup
+	tk.HasPlan("select id+1, c from t where id = 6", "IndexLookUp")
+	tk.MustQuery("select id+1, c from t use index(id) where id = 6").Check(testkit.Rows("7 6"))
+	require.True(t, tk.Session().GetSessionVars().StmtCtx.ReadFromTableCache)
+	tk.MustQuery("select id+1, c from t use index(id) where id = 4").Check(testkit.Rows("5 4"))
+	require.True(t, tk.Session().GetSessionVars().StmtCtx.ReadFromTableCache)
+
+	// Index Reader
+	tk.HasPlan("select id from t where id = 6", "IndexReader")
+	tk.MustQuery("select id from t use index(id) where id = 6").Check(testkit.Rows("6"))
+	require.True(t, tk.Session().GetSessionVars().StmtCtx.ReadFromTableCache)
+	tk.MustQuery("select id from t use index(id) where id = 4").Check(testkit.Rows("4"))
+	require.True(t, tk.Session().GetSessionVars().StmtCtx.ReadFromTableCache)
+
+	tk.MustExec("rollback")
+}
+
+func TestIssue36903(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t_vwvgdc")
+
+	tk.MustExec("CREATE TABLE t_vwvgdc (wkey int, pkey int NOT NULL, c_rdsfbc double DEFAULT NULL, PRIMARY KEY (`pkey`));")
+	tk.MustExec("insert into t_vwvgdc values (2, 15000, 61.75);")
+	tk.MustExec("BEGIN OPTIMISTIC;")
+	tk.MustExec("insert into t_vwvgdc (wkey, pkey, c_rdsfbc) values (155, 228000, 99.50);")
+	tk.MustQuery("select pkey from t_vwvgdc where 0 <> 0 union select pkey from t_vwvgdc;")
+}
+
+func BenchmarkUnionScanRead(b *testing.B) {
+	store := testkit.CreateMockStore(b)
+
+	tk := testkit.NewTestKit(b, store)
+	tk.MustExec("use test")
+	tk.MustExec(`create table t_us (
+c1 varchar(10),
+c2 varchar(30),
+c3 varchar(1),
+c4 varchar(12),
+c5 varchar(10),
+c6 datetime);`)
+	tk.MustExec(`begin;`)
+	for i := 0; i < 8000; i++ {
+		tk.MustExec("insert into t_us values ('54321', '1234', '1', '000000', '7518', '2014-05-08')")
+	}
+
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		tk.MustQuery("select * from t_us where c1 = '12345'").Check(testkit.Rows())
+	}
+	b.StopTimer()
+}
+
+func TestBenchDaily(t *testing.T) {
+	benchdaily.Run(
+		executor.BenchmarkReadLastLinesOfHugeLine,
+		BenchmarkUnionScanRead,
+	)
+}
+>>>>>>> 81a93a697... executor, util: fix UnionScan Next() skip reading data when passed chunk capacity is 0 (#36961)
diff --git a/util/chunk/chunk.go b/util/chunk/chunk.go
index 08668b3cb690a..30705e32d4e26 100644
--- a/util/chunk/chunk.go
+++ b/util/chunk/chunk.go
@@ -308,7 +308,11 @@ func reCalcCapacity(c *Chunk, maxChunkSize int) int {
 	if c.NumRows() < c.capacity {
 		return c.capacity
 	}
-	return mathutil.Min(c.capacity*2, maxChunkSize)
+	newCapacity := c.capacity * 2
+	if newCapacity == 0 {
+		newCapacity = InitialCapacity
+	}
+	return mathutil.Min(newCapacity, maxChunkSize)
 }
 
 // Capacity returns the capacity of the Chunk.