ddl, domain: handle the corner case that putting the MDL key to etcd …

…failed (#39418)

close #39416

ddl/db_test.go

@@ -1763,3 +1763,15 @@ func TestDDLBlockedCreateView(t *testing.T) {
 	dom.DDL().SetHook(hook)
 	tk.MustExec("alter table t modify column a char(10)")
 }
+
+func TestMDLPutETCDFail(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t(a int)")
+
+	require.NoError(t, failpoint.Enable("github.com/pingcap/tidb/ddl/putEtcdFailed", `return(true)`))
+	defer require.NoError(t, failpoint.Disable("github.com/pingcap/tidb/ddl/putEtcdFailed"))
+	tk.MustExec("alter table t add column b int")
+}

ddl/mock.go

@@ -66,6 +66,12 @@ func (s *MockSchemaSyncer) WatchGlobalSchemaVer(context.Context) {}
 
 // UpdateSelfVersion implements SchemaSyncer.UpdateSelfVersion interface.
 func (s *MockSchemaSyncer) UpdateSelfVersion(ctx context.Context, jobID int64, version int64) error {
+	failpoint.Inject("putEtcdFailed", func() {
+		if mockDDLErrOnce < 3 {
+			mockDDLErrOnce++
+			failpoint.Return(errors.New("mock putEtcdFailed"))
+		}
+	})
 	if variable.EnableMDL.Load() {
 		s.mdlSchemaVersions.Store(jobID, version)
 	} else {

domain/domain.go

@@ -724,6 +724,7 @@ func (do *Domain) mdlCheckLoop() {
 				err := do.ddl.SchemaSyncer().UpdateSelfVersion(context.Background(), jobID, ver)
 				if err != nil {
 					logutil.BgLogger().Warn("update self version failed", zap.Error(err))
+					jobNeedToSync = true
 				} else {
 					jobCache[jobID] = ver
 				}