Fix comments; remove unnecessary deep copy (#31945)

Co-authored-by: MyonKeminta <MyonKeminta@users.noreply.github.com>

store/driver/txn/txn_driver.go

@@ -292,18 +292,16 @@ func (txn *tikvTxn) extractKeyExistsErr(key kv.Key) error {
 	return extractKeyExistsErrFromIndex(key, value, tblInfo, indexID)
 }
 
-// SetAssertion sets a assertion for the key operation.
+// SetAssertion sets an assertion for the key operation.
 func (txn *tikvTxn) SetAssertion(key []byte, assertion ...kv.FlagsOp) error {
-	// Deep copy the key since it's memory is referenced from union store and overwrite change later.
-	key1 := append([]byte{}, key...)
-	f, err := txn.GetUnionStore().GetMemBuffer().GetFlags(key1)
+	f, err := txn.GetUnionStore().GetMemBuffer().GetFlags(key)
 	if err != nil && !tikverr.IsErrNotFound(err) {
 		return err
 	}
 	if err == nil && f.HasAssertionFlags() {
 		return nil
 	}
-	txn.GetUnionStore().GetMemBuffer().UpdateFlags(key1, getTiKVFlagsOps(assertion)...)
+	txn.GetUnionStore().GetMemBuffer().UpdateFlags(key, getTiKVFlagsOps(assertion)...)
 	return nil
 }
 

table/tables/tables_test.go

@@ -768,8 +768,6 @@ func TestConstraintCheckForOptimisticUntouched(t *testing.T) {
 func TestTxnAssertion(t *testing.T) {
 	store, clean := testkit.CreateMockStore(t)
 	defer clean()
-	// TODO: Locks produced by this test may be left without cleaning up, causing the test runs longer than expected.
-	// This is caused by that client-go didn't clean up the transaction when `initKeysAndMutations` returns error.
 
 	se, err := session.CreateSession4Test(store)
 	se.SetConnectionID(1)