VReplication: Address SwitchTraffic bugs around replication lag and cancel on error

go/test/endtoend/vreplication/cluster_test.go

@@ -856,7 +856,7 @@ func (vc *VitessCluster) getVttabletsInKeyspace(t *testing.T, cell *Cell, ksName
 	tablets := make(map[string]*cluster.VttabletProcess)
 	for _, shard := range keyspace.Shards {
 		for _, tablet := range shard.Tablets {
-			if tablet.Vttablet.GetTabletStatus() == "SERVING" {
+			if tablet.Vttablet.GetTabletStatus() == "SERVING" && (tabletType == "" || strings.EqualFold(tablet.Vttablet.GetTabletType(), tabletType)) {
 				log.Infof("Serving status of tablet %s is %s, %s", tablet.Name, tablet.Vttablet.ServingStatus, tablet.Vttablet.GetTabletStatus())
 				tablets[tablet.Name] = tablet.Vttablet
 			}

go/test/endtoend/vreplication/vreplication_test.go

@@ -826,6 +826,11 @@ func shardCustomer(t *testing.T, testReverse bool, cells []*Cell, sourceCellOrAl
 			shardNames = append(shardNames, shardName)
 		}
 		testSwitchTrafficPermissionChecks(t, workflowType, sourceKs, shardNames, targetKs, workflow)
+
+		testSwitchWritesErrorHandling(t, []*cluster.VttabletProcess{productTab}, []*cluster.VttabletProcess{customerTab1, customerTab2},
+			workflow, workflowType)
+
+		// Now let's confirm that it works as expected with an error.
 		switchWrites(t, workflowType, ksWorkflow, false)
 
 		checkThatVDiffFails(t, targetKs, workflow)
@@ -1057,6 +1062,7 @@ func reshard(t *testing.T, ksName string, tableName string, workflow string, sou
 		require.NoError(t, vc.AddShards(t, cells, keyspace, targetShards, defaultReplicas, defaultRdonly, tabletIDBase, targetKsOpts))
 
 		tablets := vc.getVttabletsInKeyspace(t, defaultCell, ksName, "primary")
+		var sourceTablets, targetTablets []*cluster.VttabletProcess
 
 		// Test multi-primary setups, like a Galera cluster, which have auto increment steps > 1.
 		for _, tablet := range tablets {
@@ -1069,9 +1075,11 @@ func reshard(t *testing.T, ksName string, tableName string, workflow string, sou
 		targetShards = "," + targetShards + ","
 		for _, tab := range tablets {
 			if strings.Contains(targetShards, ","+tab.Shard+",") {
+				targetTablets = append(targetTablets, tab)
 				log.Infof("Waiting for vrepl to catch up on %s since it IS a target shard", tab.Shard)
 				catchup(t, tab, workflow, "Reshard")
 			} else {
+				sourceTablets = append(sourceTablets, tab)
 				log.Infof("Not waiting for vrepl to catch up on %s since it is NOT a target shard", tab.Shard)
 				continue
 			}
@@ -1085,6 +1093,10 @@ func reshard(t *testing.T, ksName string, tableName string, workflow string, sou
 		if dryRunResultSwitchWrites != nil {
 			reshardAction(t, "SwitchTraffic", workflow, ksName, "", "", callNames, "primary", "--dry-run")
 		}
+		if tableName == "customer" {
+			testSwitchWritesErrorHandling(t, sourceTablets, targetTablets, workflow, "reshard")
+		}
+		// Now let's confirm that it works as expected with an error.
 		reshardAction(t, "SwitchTraffic", workflow, ksName, "", "", callNames, "primary")
 		reshardAction(t, "Complete", workflow, ksName, "", "", "", "")
 		for tabletName, count := range counts {
@@ -1656,6 +1668,140 @@ func testSwitchTrafficPermissionChecks(t *testing.T, workflowType, sourceKeyspac
 	})
 }
 
+// testSwitchWritesErrorHandling confirms that switching writes works as expected
+// in the face of vreplication lag (canSwitch() precheck) and when canceling the
+// switch due to replication failing to catch up in time.
+// The workflow MUST be migrating the customer table from the source to the
+// target keyspace AND the workflow must currently have reads switched but not
+// writes.
+func testSwitchWritesErrorHandling(t *testing.T, sourceTablets, targetTablets []*cluster.VttabletProcess, workflow, workflowType string) {
+	t.Run("validate switch writes error handling", func(t *testing.T) {
+		vtgateConn := getConnection(t, vc.ClusterConfig.hostname, vc.ClusterConfig.vtgateMySQLPort)
+		defer vtgateConn.Close()
+		require.NotZero(t, len(sourceTablets), "no source tablets provided")
+		require.NotZero(t, len(targetTablets), "no target tablets provided")
+		sourceKs := sourceTablets[0].Keyspace
+		targetKs := targetTablets[0].Keyspace
+		ksWorkflow := fmt.Sprintf("%s.%s", targetKs, workflow)
+		var err error
+		sourceConns := make([]*mysql.Conn, len(sourceTablets))
+		for i, tablet := range sourceTablets {
+			sourceConns[i], err = tablet.TabletConn(tablet.Keyspace, true)
+			require.NoError(t, err)
+			defer sourceConns[i].Close()
+		}
+		targetConns := make([]*mysql.Conn, len(targetTablets))
+		for i, tablet := range targetTablets {
+			targetConns[i], err = tablet.TabletConn(tablet.Keyspace, true)
+			require.NoError(t, err)
+			defer targetConns[i].Close()
+		}
+		startingTestRowID := 10000000
+		numTestRows := 100
+		addTestRows := func() {
+			for i := 0; i < numTestRows; i++ {
+				execVtgateQuery(t, vtgateConn, sourceTablets[0].Keyspace, fmt.Sprintf("insert into customer (cid, name) values (%d, 'laggingCustomer')",
+					startingTestRowID+i))
+			}
+		}
+		deleteTestRows := func() {
+			execVtgateQuery(t, vtgateConn, sourceTablets[0].Keyspace, fmt.Sprintf("delete from customer where cid >= %d", startingTestRowID))
+		}
+		addIndex := func() {
+			for _, targetConn := range targetConns {
+				execQuery(t, targetConn, "set session sql_mode=''")
+				execQuery(t, targetConn, "alter table customer add unique index name_idx (name)")
+			}
+		}
+		dropIndex := func() {
+			for _, targetConn := range targetConns {
+				execQuery(t, targetConn, "alter table customer drop index name_idx")
+			}
+		}
+		lockTargetTable := func() {
+			for _, targetConn := range targetConns {
+				execQuery(t, targetConn, "lock table customer read")
+			}
+		}
+		unlockTargetTable := func() {
+			for _, targetConn := range targetConns {
+				execQuery(t, targetConn, "unlock tables")
+			}
+		}
+		cleanupTestData := func() {
+			dropIndex()
+			deleteTestRows()
+		}
+		restartWorkflow := func() {
+			err = vc.VtctldClient.ExecuteCommand("workflow", "--keyspace", targetKs, "start", "--workflow", workflow)
+			require.NoError(t, err, "failed to start workflow: %v", err)
+		}
+		waitForTargetToCatchup := func() {
+			waitForWorkflowState(t, vc, ksWorkflow, binlogdatapb.VReplicationWorkflowState_Running.String())
+			waitForNoWorkflowLag(t, vc, targetKs, workflow)
+		}
+
+		// First let's test that the prechecks work as expected. We ALTER
+		// the table on the target shards to add a unique index on the name
+		// field.
+		addIndex()
+		// Then we replicate some test rows across the target shards by
+		// inserting them in the source keyspace.
+		addTestRows()
+		// Now the workflow should go into the error state and the lag should
+		// start to climb. So we sleep for twice the max lag duration that we
+		// will set for the SwitchTraffic call.
+		lagDuration := 3 * time.Second
+		time.Sleep(lagDuration * 3)
+		out, err := vc.VtctldClient.ExecuteCommandWithOutput(workflowType, "--workflow", workflow, "--target-keyspace", targetKs,
+			"SwitchTraffic", "--tablet-types=primary", "--timeout=30s", "--max-replication-lag-allowed", lagDuration.String())
+		// It should fail in the canSwitch() precheck.
+		require.Error(t, err)
+		require.Regexp(t, fmt.Sprintf(".*cannot switch traffic for workflow %s at this time: replication lag [0-9]+s is higher than allowed lag %s.*",
+			workflow, lagDuration.String()), out)
+		require.NotContains(t, out, "cancel migration failed")
+		// Confirm that queries still work fine.
+		execVtgateQuery(t, vtgateConn, sourceKs, "select * from customer limit 1")
+		cleanupTestData()
+		// We have to restart the workflow again as the duplicate key error
+		// is a permanent/terminal one.
+		restartWorkflow()
+		waitForTargetToCatchup()
+
+		// Now let's test that the cancel works by setting the command timeout
+		// to a fraction (6s) of the default max repl lag duration (30s). First
+		// we lock the customer table on the target tablets so that we cannot
+		// apply the INSERTs and catch up.
+		lockTargetTable()
+		addTestRows()
+		timeout := lagDuration * 2 // 6s
+		// Use the default max-replication-lag-allowed value of 30s.
+		// We run the command in a goroutine so that we can unblock things
+		// after the timeout is reached -- as the vplayer query is blocking
+		// on the table lock in the MySQL layer.
+		wg := sync.WaitGroup{}
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			out, err = vc.VtctldClient.ExecuteCommandWithOutput(workflowType, "--workflow", workflow, "--target-keyspace", targetKs,
+				"SwitchTraffic", "--tablet-types=primary", "--timeout", timeout.String())
+		}()
+		time.Sleep(timeout)
+		// Now we can unblock things and let it continue.
+		unlockTargetTable()
+		wg.Wait()
+		// It should fail due to the command context timeout and we should
+		// successfully cancel.
+		require.Error(t, err)
+		require.Contains(t, out, "failed to sync up replication between the source and target")
+		require.NotContains(t, out, "cancel migration failed")
+		// Confirm that queries still work fine.
+		execVtgateQuery(t, vtgateConn, sourceKs, "select * from customer limit 1")
+		deleteTestRows()
+		waitForTargetToCatchup()
+	})
+}
+
 // restartWorkflow confirms that a workflow can be successfully
 // stopped and started.
 func restartWorkflow(t *testing.T, ksWorkflow string) {

go/vt/vtctl/workflow/server.go

@@ -2915,8 +2915,10 @@ func (s *Server) switchWrites(ctx context.Context, req *vtctldatapb.WorkflowSwit
 			return handleError("failed to migrate the workflow streams", err)
 		}
 		if cancel {
-			sw.cancelMigration(ctx, sm)
-			return 0, sw.logs(), nil
+			if cerr := sw.cancelMigration(ctx, sm); cerr != nil {
+				err = vterrors.Errorf(vtrpcpb.Code_CANCELED, "%v\n\n%v", err, cerr)
+			}
+			return 0, sw.logs(), err
 		}
 
 		// We stop writes on the source before stopping the source streams so that the catchup time
@@ -2928,7 +2930,9 @@ func (s *Server) switchWrites(ctx context.Context, req *vtctldatapb.WorkflowSwit
 		// we actually stop them.
 		ts.Logger().Infof("Stopping source writes")
 		if err := sw.stopSourceWrites(ctx); err != nil {
-			sw.cancelMigration(ctx, sm)
+			if cerr := sw.cancelMigration(ctx, sm); cerr != nil {
+				err = vterrors.Errorf(vtrpcpb.Code_CANCELED, "%v\n\n%v", err, cerr)
+			}
 			return handleError(fmt.Sprintf("failed to stop writes in the %s keyspace", ts.SourceKeyspaceName()), err)
 		}
 
@@ -2946,7 +2950,9 @@ func (s *Server) switchWrites(ctx context.Context, req *vtctldatapb.WorkflowSwit
 					ts.Logger().Errorf("stream in stopStreams: key %s shard %s stream %+v", key, stream.BinlogSource.Shard, stream.BinlogSource)
 				}
 			}
-			sw.cancelMigration(ctx, sm)
+			if cerr := sw.cancelMigration(ctx, sm); cerr != nil {
+				err = vterrors.Errorf(vtrpcpb.Code_CANCELED, "%v\n\n%v", err, cerr)
+			}
 			return handleError(fmt.Sprintf("failed to stop the workflow streams in the %s keyspace", ts.SourceKeyspaceName()), err)
 		}
 
@@ -2956,7 +2962,9 @@ func (s *Server) switchWrites(ctx context.Context, req *vtctldatapb.WorkflowSwit
 			// the tablet's deny list check and the first mysqld side table lock.
 			for cnt := 1; cnt <= lockTablesCycles; cnt++ {
 				if err := ts.executeLockTablesOnSource(ctx); err != nil {
-					sw.cancelMigration(ctx, sm)
+					if cerr := sw.cancelMigration(ctx, sm); cerr != nil {
+						err = vterrors.Errorf(vtrpcpb.Code_CANCELED, "%v\n\n%v", err, cerr)
+					}
 					return handleError(fmt.Sprintf("failed to execute LOCK TABLES (attempt %d of %d) on sources", cnt, lockTablesCycles), err)
 				}
 				// No need to UNLOCK the tables as the connection was closed once the locks were acquired
@@ -2977,7 +2985,9 @@ func (s *Server) switchWrites(ctx context.Context, req *vtctldatapb.WorkflowSwit
 		}
 		ts.Logger().Infof("Waiting for streams to catchup")
 		if err := sw.waitForCatchup(ctx, waitTimeout); err != nil {
-			sw.cancelMigration(ctx, sm)
+			if cerr := sw.cancelMigration(ctx, sm); cerr != nil {
+				err = vterrors.Errorf(vtrpcpb.Code_CANCELED, "%v\n\n%v", err, cerr)
+			}
 			return handleError("failed to sync up replication between the source and target", err)
 		}
 
@@ -2986,7 +2996,9 @@ func (s *Server) switchWrites(ctx context.Context, req *vtctldatapb.WorkflowSwit
 		}
 		ts.Logger().Infof("Migrating streams")
 		if err := sw.migrateStreams(ctx, sm); err != nil {
-			sw.cancelMigration(ctx, sm)
+			if cerr := sw.cancelMigration(ctx, sm); cerr != nil {
+				err = vterrors.Errorf(vtrpcpb.Code_CANCELED, "%v\n\n%v", err, cerr)
+			}
 			return handleError("failed to migrate the workflow streams", err)
 		}
 
@@ -2995,7 +3007,9 @@ func (s *Server) switchWrites(ctx context.Context, req *vtctldatapb.WorkflowSwit
 		}
 		ts.Logger().Infof("Resetting sequences")
 		if err := sw.resetSequences(ctx); err != nil {
-			sw.cancelMigration(ctx, sm)
+			if cerr := sw.cancelMigration(ctx, sm); cerr != nil {
+				err = vterrors.Errorf(vtrpcpb.Code_CANCELED, "%v\n\n%v", err, cerr)
+			}
 			return handleError("failed to reset the sequences", err)
 		}
 
@@ -3004,7 +3018,9 @@ func (s *Server) switchWrites(ctx context.Context, req *vtctldatapb.WorkflowSwit
 		}
 		ts.Logger().Infof("Creating reverse streams")
 		if err := sw.createReverseVReplication(ctx); err != nil {
-			sw.cancelMigration(ctx, sm)
+			if cerr := sw.cancelMigration(ctx, sm); cerr != nil {
+				err = vterrors.Errorf(vtrpcpb.Code_CANCELED, "%v\n\n%v", err, cerr)
+			}
 			return handleError("failed to create the reverse vreplication streams", err)
 		}
 
@@ -3019,7 +3035,9 @@ func (s *Server) switchWrites(ctx context.Context, req *vtctldatapb.WorkflowSwit
 			initSeqCtx, cancel := context.WithTimeout(ctx, waitTimeout/2)
 			defer cancel()
 			if err := sw.initializeTargetSequences(initSeqCtx, sequenceMetadata); err != nil {
-				sw.cancelMigration(ctx, sm)
+				if cerr := sw.cancelMigration(ctx, sm); cerr != nil {
+					err = vterrors.Errorf(vtrpcpb.Code_CANCELED, "%v\n\n%v", err, cerr)
+				}
 				return handleError(fmt.Sprintf("failed to initialize the sequences used in the %s keyspace", ts.TargetKeyspaceName()), err)
 			}
 		}
@@ -3069,15 +3087,14 @@ func (s *Server) canSwitch(ctx context.Context, ts *trafficSwitcher, maxAllowedR
 	if err != nil {
 		return "", err
 	}
+	if wf.MaxVReplicationTransactionLag > maxAllowedReplLagSecs {
+		return fmt.Sprintf(cannotSwitchHighLag, wf.MaxVReplicationTransactionLag, maxAllowedReplLagSecs), nil
+	}
 	for _, stream := range wf.ShardStreams {
 		for _, st := range stream.GetStreams() {
 			if st.Message == Frozen {
 				return cannotSwitchFrozen, nil
 			}
-			// If no new events have been replicated after the copy phase then it will be 0.
-			if vreplLag := time.Now().Unix() - st.TimeUpdated.Seconds; vreplLag > maxAllowedReplLagSecs {
-				return fmt.Sprintf(cannotSwitchHighLag, vreplLag, maxAllowedReplLagSecs), nil
-			}
 			switch st.State {
 			case binlogdatapb.VReplicationWorkflowState_Copying.String():
 				return cannotSwitchCopyIncomplete, nil

go/vt/vtctl/workflow/stream_migrator.go

@@ -203,12 +203,15 @@ func (sm *StreamMigrator) Templates() []*VReplicationStream {
 }
 
 // CancelStreamMigrations cancels the stream migrations.
-func (sm *StreamMigrator) CancelStreamMigrations(ctx context.Context) {
+func (sm *StreamMigrator) CancelStreamMigrations(ctx context.Context) error {
 	if sm.streams == nil {
-		return
+		return nil
 	}
+	errs := &concurrency.AllErrorRecorder{}
 
-	_ = sm.deleteTargetStreams(ctx)
+	if err := sm.deleteTargetStreams(ctx); err != nil {
+		errs.RecordError(fmt.Errorf("could not delete target streams: %v", err))
+	}
 
 	// Restart the source streams, but leave the Reshard workflow's reverse
 	// variant stopped.
@@ -221,8 +224,13 @@ func (sm *StreamMigrator) CancelStreamMigrations(ctx context.Context) {
 		return err
 	})
 	if err != nil {
+		errs.RecordError(fmt.Errorf("could not restart source streams: %v", err))
 		sm.logger.Errorf("Cancel stream migrations failed: could not restart source streams: %v", err)
 	}
+	if errs.HasErrors() {
+		return errs.AggrError(vterrors.Aggregate)
+	}
+	return nil
 }
 
 // MigrateStreams migrates N streams

go/vt/vtctl/workflow/switcher.go

@@ -124,8 +124,8 @@ func (r *switcher) stopStreams(ctx context.Context, sm *StreamMigrator) ([]strin
 	return sm.StopStreams(ctx)
 }
 
-func (r *switcher) cancelMigration(ctx context.Context, sm *StreamMigrator) {
-	r.ts.cancelMigration(ctx, sm)
+func (r *switcher) cancelMigration(ctx context.Context, sm *StreamMigrator) error {
+	return r.ts.cancelMigration(ctx, sm)
 }
 
 func (r *switcher) lockKeyspace(ctx context.Context, keyspace, action string, opts ...topo.LockOption) (context.Context, func(*error), error) {

go/vt/vtctl/workflow/switcher_dry_run.go

@@ -301,8 +301,9 @@ func (dr *switcherDryRun) stopStreams(ctx context.Context, sm *StreamMigrator) (
 	return nil, nil
 }
 
-func (dr *switcherDryRun) cancelMigration(ctx context.Context, sm *StreamMigrator) {
+func (dr *switcherDryRun) cancelMigration(ctx context.Context, sm *StreamMigrator) error {
 	dr.drLog.Log("Cancel migration as requested")
+	return nil
 }
 
 func (dr *switcherDryRun) lockKeyspace(ctx context.Context, keyspace, _ string, _ ...topo.LockOption) (context.Context, func(*error), error) {

go/vt/vtctl/workflow/switcher_interface.go

@@ -27,7 +27,7 @@ import (
 
 type iswitcher interface {
 	lockKeyspace(ctx context.Context, keyspace, action string, opts ...topo.LockOption) (context.Context, func(*error), error)
-	cancelMigration(ctx context.Context, sm *StreamMigrator)
+	cancelMigration(ctx context.Context, sm *StreamMigrator) error
 	stopStreams(ctx context.Context, sm *StreamMigrator) ([]string, error)
 	stopSourceWrites(ctx context.Context) error
 	waitForCatchup(ctx context.Context, filteredReplicationWaitTime time.Duration) error