Online DDL: detect vreplication errors via vreplication_log history

go/test/endtoend/onlineddl/vrepl/onlineddl_vrepl_test.go

@@ -80,6 +80,9 @@ var (
 		ALTER TABLE %s
 			DROP PRIMARY KEY,
 			DROP COLUMN vrepl_col`
+	alterTableFailedVreplicationStatement = `
+			ALTER TABLE %s
+				ADD UNIQUE KEY test_val_uidx (test_val)`
 	// We will run this query while throttling vreplication
 	alterTableThrottlingStatement = `
 		ALTER TABLE %s
@@ -456,6 +459,19 @@ func TestVreplSchemaChanges(t *testing.T) {
 		onlineddl.CheckMigrationArtifacts(t, &vtParams, shards, uuid, true)
 		// migration will fail again
 	})
+	t.Run("failed migration due to vreplication", func(t *testing.T) {
+		insertRows(t, 2)
+		uuid := testOnlineDDLStatement(t, alterTableFailedVreplicationStatement, "online", providedUUID, providedMigrationContext, "vtgate", "vrepl_col", "", false)
+		onlineddl.WaitForMigrationStatus(t, &vtParams, shards, uuid, normalMigrationWait, schema.OnlineDDLStatusComplete, schema.OnlineDDLStatusFailed)
+		onlineddl.CheckMigrationStatus(t, &vtParams, shards, uuid, schema.OnlineDDLStatusFailed)
+
+		rs := onlineddl.ReadMigrations(t, &vtParams, uuid)
+		require.NotNil(t, rs)
+		for _, row := range rs.Named().Rows {
+			message := row["message"].ToString()
+			assert.Contains(t, message, "vreplication: terminal error:", "migration row: %v", row)
+		}
+	})
 	t.Run("cancel all migrations: nothing to cancel", func(t *testing.T) {
 		// no migrations pending at this time
 		time.Sleep(10 * time.Second)

go/vt/vttablet/onlineddl/executor.go

@@ -60,6 +60,7 @@ import (
 	"vitess.io/vitess/go/vt/topo"
 	"vitess.io/vitess/go/vt/topo/topoproto"
 	"vitess.io/vitess/go/vt/vterrors"
+	"vitess.io/vitess/go/vt/vttablet/tabletmanager/vreplication"
 	"vitess.io/vitess/go/vt/vttablet/tabletserver/connpool"
 	"vitess.io/vitess/go/vt/vttablet/tabletserver/tabletenv"
 	"vitess.io/vitess/go/vt/vttablet/tabletserver/throttle"
@@ -3485,6 +3486,28 @@ func (e *Executor) readVReplStream(ctx context.Context, uuid string, okIfMissing
 	if err := prototext.Unmarshal([]byte(s.source), s.bls); err != nil {
 		return nil, err
 	}
+	{
+		// It's possible that an earlier error was overshadowed by a new non-error `message` values.
+		// Let's read _vt.vreplication_log to see whether there's any terminal errors in vreplication's history.
+		query, err := sqlparser.ParseAndBind(sqlReadVReplLogErrors,
+			sqltypes.Int32BindVariable(s.id),
+			sqltypes.StringBindVariable(vreplication.TerminalErrorIndicator),
+		)
+		if err != nil {
+			return nil, err
+		}
+		r, err := e.execQuery(ctx, query)
+		if err != nil {
+			return nil, err
+		}
+		// The query has LIMIT 1, ie returns at most one row
+		if row := r.Named().Row(); row != nil {
+			s.state = binlogdatapb.VReplicationWorkflowState_Error
+			if message := row.AsString("message", ""); message != "" {
+				s.message = "vreplication: " + message
+			}
+		}
+	}
 	return s, nil
 }
 

go/vt/vttablet/onlineddl/schema.go

@@ -515,6 +515,20 @@ const (
 		WHERE
 			workflow=%a
 		`
+	sqlReadVReplLogErrors = `SELECT
+			state,
+			message
+		FROM _vt.vreplication_log
+		WHERE
+			vrepl_id=%a
+			AND (
+				state='Error'
+				OR locate (concat(%a, ':'), message) = 1
+			)
+		ORDER BY
+			id DESC
+		LIMIT 1
+	`
 	sqlReadCountCopyState = `SELECT
 			count(*) as cnt
 		FROM

go/vt/vttablet/tabletmanager/vreplication/controller.go

@@ -47,6 +47,9 @@ const (
 	// give up and return an error message that the user
 	// can see and act upon if needed.
 	tabletPickerRetries = 5
+
+	// Prepended to the message to indicate that it is a terminal error.
+	TerminalErrorIndicator = "terminal error"
 )
 
 // controller is created by Engine. Members are initialized upfront.
@@ -305,7 +308,7 @@ func (ct *controller) runBlp(ctx context.Context) (err error) {
 		if (err != nil && vr.WorkflowSubType == int32(binlogdatapb.VReplicationWorkflowSubType_AtomicCopy)) ||
 			isUnrecoverableError(err) ||
 			!ct.lastWorkflowError.ShouldRetry() {
-
+			err = vterrors.Wrapf(err, TerminalErrorIndicator)
 			if errSetState := vr.setState(binlogdatapb.VReplicationWorkflowState_Error, err.Error()); errSetState != nil {
 				log.Errorf("INTERNAL: unable to setState() in controller: %v. Could not set error text to: %v.", errSetState, err)
 				return err // yes, err and not errSetState.

go/vt/vttablet/tabletmanager/vreplication/vplayer_flaky_test.go

@@ -1782,7 +1782,7 @@ func TestPlayerDDL(t *testing.T) {
 	expectDBClientQueries(t, qh.Expect(
 		"alter table t1 add column val2 varchar(128)",
 		"/update _vt.vreplication set message='error applying event: Duplicate",
-		"/update _vt.vreplication set state='Error', message='error applying event: Duplicate",
+		"/update _vt.vreplication set state='Error', message='terminal error: error applying event: Duplicate",
 	))
 	cancel()