VRep: improve few error/log messages

go/vt/vttablet/tabletserver/vstreamer/uvstreamer.go

@@ -320,7 +320,7 @@ func (uvs *uvstreamer) setStreamStartPosition() error {
 		return vterrors.Wrap(err, "could not decode position")
 	}
 	if !curPos.AtLeast(pos) {
-		return fmt.Errorf("requested position %v is ahead of current position %v", mysql.EncodePosition(pos), mysql.EncodePosition(curPos))
+		return fmt.Errorf("GTIDSet Mismatch: requested source position:%v, current target vrep position: %v", mysql.EncodePosition(pos), mysql.EncodePosition(curPos))
 	}
 	uvs.pos = pos
 	return nil

go/vt/vttablet/tabletserver/vstreamer/vstreamer_test.go

@@ -1513,7 +1513,7 @@ func TestNoFutureGTID(t *testing.T) {
 	}()
 	defer close(ch)
 	err = vstream(ctx, t, future, nil, nil, ch)
-	want := "is ahead of current position"
+	want := "GTIDSet Mismatch"
 	if err == nil || !strings.Contains(err.Error(), want) {
 		t.Errorf("err: %v, must contain %s", err, want)
 	}

go/vt/wrangler/vdiff.go

@@ -71,6 +71,9 @@ type vdiff struct {
 	// The source and target keyspaces are pulled from ts.
 	sources map[string]*shardStreamer
 	targets map[string]*shardStreamer
+
+	workflow       string
+	targetKeyspace string
 }
 
 // tableDiffer performs a diff for one table in the workflow.
@@ -153,6 +156,8 @@ func (wr *Wrangler) VDiff(ctx context.Context, targetKeyspace, workflow, sourceC
 		tabletTypesStr: tabletTypesStr,
 		sources:        make(map[string]*shardStreamer),
 		targets:        make(map[string]*shardStreamer),
+		workflow:       workflow,
+		targetKeyspace: targetKeyspace,
 	}
 	for shard, source := range ts.sources {
 		df.sources[shard] = &shardStreamer{
@@ -545,7 +550,13 @@ func (df *vdiff) startQueryStreams(ctx context.Context, keyspace string, partici
 	defer cancel()
 	return df.forAll(participants, func(shard string, participant *shardStreamer) error {
 		// Iteration for each participant.
+		if participant.position.IsZero() {
+			return fmt.Errorf("workflow %s.%s: stream has not started on tablet %s", df.targetKeyspace, df.workflow, participant.master.Alias.String())
+		}
 		if err := df.ts.wr.tmc.WaitForPosition(waitCtx, participant.tablet, mysql.EncodePosition(participant.position)); err != nil {
+			if err.Error() == "context deadline exceeded" {
+				return fmt.Errorf("VDiff timed out for tablet %v: you may want to increase it with the flag -filtered_replication_wait_time=<timeoutSeconds>", topoproto.TabletAliasString(participant.tablet.Alias))
+			}
 			return vterrors.Wrapf(err, "WaitForPosition for tablet %v", topoproto.TabletAliasString(participant.tablet.Alias))
 		}
 		participant.result = make(chan *sqltypes.Result, 1)
@@ -795,7 +806,7 @@ func (td *tableDiffer) diff(ctx context.Context, wr *Wrangler) (*DiffReport, err
 		if targetRow == nil {
 			// no more rows from the target
 			// we know we have rows from source, drain, update count
-			wr.Logger().Errorf("Draining extra row(s) found on the source starting with: %v", sourceRow)
+			wr.Logger().Warningf("Draining extra row(s) found on the source starting with: %v", sourceRow)
 			count, err := sourceExecutor.drain(ctx)
 			if err != nil {
 				return nil, err

go/vt/wrangler/vdiff_test.go

@@ -891,7 +891,7 @@ func TestVDiffReplicationWait(t *testing.T) {
 	env.tablets[201].setResults("select c1, c2 from t1 order by c1 asc", vdiffTargetMasterPosition, target)
 
 	_, err := env.wr.VDiff(context.Background(), "target", env.workflow, env.cell, env.cell, "replica", 0*time.Second, "")
-	require.EqualError(t, err, "startQueryStreams(sources): WaitForPosition for tablet cell-0000000101: context deadline exceeded")
+	require.EqualError(t, err, "startQueryStreams(sources): VDiff timed out for tablet cell-0000000101: you may want to increase it with the flag -filtered_replication_wait_time=<timeoutSeconds>")
 }
 
 func TestVDiffFindPKs(t *testing.T) {