diff --git a/dm/pkg/utils/common.go b/dm/pkg/utils/common.go
index 9c5ddfc7ada..25c4ecb348a 100644
--- a/dm/pkg/utils/common.go
+++ b/dm/pkg/utils/common.go
@@ -37,6 +37,10 @@ import (
 	"github.com/pingcap/tiflow/dm/pkg/terror"
 )
 
+func init() {
+	ZeroSessionCtx = NewSessionCtx(nil)
+}
+
 // TrimCtrlChars returns a slice of the string s with all leading
 // and trailing control characters removed.
 func TrimCtrlChars(s string) string {
@@ -322,11 +326,12 @@ func (se *session) GetBuiltinFunctionUsage() map[string]uint32 {
 	return se.builtinFunctionUsage
 }
 
+// ZeroSessionCtx is used when the session variables is not important.
+var ZeroSessionCtx sessionctx.Context
+
 // NewSessionCtx return a session context with specified session variables.
 func NewSessionCtx(vars map[string]string) sessionctx.Context {
 	variables := variable.NewSessionVars()
-	variables.Rng.SetSeed1(0)
-	variables.Rng.SetSeed2(0)
 	for k, v := range vars {
 		_ = variables.SetSystemVar(k, v)
 		if strings.EqualFold(k, "time_zone") {
diff --git a/pkg/sqlmodel/causality_test.go b/pkg/sqlmodel/causality_test.go
index 2464856169a..4a49e95640e 100644
--- a/pkg/sqlmodel/causality_test.go
+++ b/pkg/sqlmodel/causality_test.go
@@ -14,6 +14,7 @@
 package sqlmodel
 
 import (
+	"sync"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -53,3 +54,20 @@ func TestCausalityKeys(t *testing.T) {
 		require.Equal(t, ca.causalityKeys, change.CausalityKeys())
 	}
 }
+
+func TestCausalityKeysNoRace(t *testing.T) {
+	t.Parallel()
+
+	source := &cdcmodel.TableName{Schema: "db", Table: "tb1"}
+	ti := mockTableInfo(t, "CREATE TABLE tb1 (c INT PRIMARY KEY, c2 INT, c3 VARCHAR(10) UNIQUE)")
+	var wg sync.WaitGroup
+	for i := 0; i < 100; i++ {
+		wg.Add(1)
+		go func() {
+			change := NewRowChange(source, nil, []interface{}{1, 2, "abc"}, []interface{}{3, 4, "abc"}, ti, nil, nil)
+			change.CausalityKeys()
+			wg.Done()
+		}()
+	}
+	wg.Wait()
+}
diff --git a/pkg/sqlmodel/multivalue.go b/pkg/sqlmodel/multivalue.go
index 6d2046d632c..3789d56c7a6 100644
--- a/pkg/sqlmodel/multivalue.go
+++ b/pkg/sqlmodel/multivalue.go
@@ -31,10 +31,12 @@ func SameTypeTargetAndColumns(lhs *RowChange, rhs *RowChange) bool {
 	if lhs.sourceTable.Schema == rhs.sourceTable.Schema && lhs.sourceTable.Table == rhs.sourceTable.Table {
 		return true
 	}
-	if lhs.targetTable.Schema != rhs.targetTable.Schema || lhs.targetTable.Table == rhs.targetTable.Table {
+	if lhs.targetTable.Schema != rhs.targetTable.Schema || lhs.targetTable.Table != rhs.targetTable.Table {
 		return false
 	}
 
+	// when the targets are the same and the sources are not the same (same group of shard tables), this piece of code
+	// is run.
 	var lhsCols, rhsCols []string
 	switch lhs.tp {
 	case RowChangeDelete:
diff --git a/pkg/sqlmodel/row_change.go b/pkg/sqlmodel/row_change.go
index e1aaadde33b..f0c8d941fb9 100644
--- a/pkg/sqlmodel/row_change.go
+++ b/pkg/sqlmodel/row_change.go
@@ -124,7 +124,7 @@ func NewRowChange(
 	if tiCtx != nil {
 		ret.tiSessionCtx = tiCtx
 	} else {
-		ret.tiSessionCtx = utils.NewSessionCtx(nil)
+		ret.tiSessionCtx = utils.ZeroSessionCtx
 	}
 
 	ret.calculateType()
diff --git a/pkg/sqlmodel/row_change_test.go b/pkg/sqlmodel/row_change_test.go
index 36da1e0e5b4..733c540cecd 100644
--- a/pkg/sqlmodel/row_change_test.go
+++ b/pkg/sqlmodel/row_change_test.go
@@ -85,7 +85,7 @@ func TestNewRowChange(t *testing.T) {
 
 	expected.targetTable = expected.sourceTable
 	expected.targetTableInfo = expected.sourceTableInfo
-	expected.tiSessionCtx = utils.NewSessionCtx(nil)
+	expected.tiSessionCtx = utils.ZeroSessionCtx
 	expected.identityInfo = nil
 	actual = NewRowChange(source, nil, []interface{}{1, 2}, []interface{}{1, 3}, sourceTI, nil, nil)
 	require.Equal(t, expected, actual)