dgraph-io/dgraph · error

Tablet predicate is empty in %+v

Error message

Tablet predicate is empty in %+v

What it means

Zero's ShouldServe RPC validates an incoming Tablet request and requires a non-empty Predicate (the key/edge being served). An empty predicate means the request is malformed — Zero cannot look up or assign ownership without it — so it errors immediately before any tablet lookup.

Source

Thrown at dgraph/cmd/zero/zero.go:690

		Member: m,
	}
	return resp, nil
}

// DeleteNamespace removes the tablets for deleted namespace from the membership state.
func (s *Server) DeleteNamespace(ctx context.Context, in *pb.DeleteNsRequest) (*pb.Status, error) {
	err := s.Node.proposeAndWait(ctx, &pb.ZeroProposal{DeleteNs: in})
	return &pb.Status{}, err
}

// ShouldServe returns the tablet serving the predicate passed in the request.
func (s *Server) ShouldServe(
	ctx context.Context, tablet *pb.Tablet) (resp *pb.Tablet, err error) {
	ctx, span := otel.Tracer("").Start(ctx, "Zero.ShouldServe")
	defer span.End()

	if tablet.Predicate == "" {
		return resp, errors.Errorf("Tablet predicate is empty in %+v", tablet)
	}
	if tablet.GroupId == 0 && !tablet.ReadOnly {
		return resp, errors.Errorf("Group ID is Zero in %+v", tablet)
	}

	// Check who is serving this tablet.
	tab := s.ServingTablet(tablet.Predicate)
	span.SetAttributes(attribute.String("tablet_predicate", tablet.Predicate))
	if tab != nil && !tablet.Force {
		// Someone is serving this tablet. Could be the caller as well.
		// The caller should compare the returned group against the group it holds to check who's
		// serving.
		return tab, nil
	}

	// Read-only requests should return an empty tablet instead of asking zero
	// to serve the predicate.
	if tablet.ReadOnly {

View on GitHub (pinned to 759e242be6)

Solutions

1. Fix the caller so the Tablet message includes the predicate (the edge/UID key) before invoking ShouldServe.
2. Upgrade alpha and Zero to matching versions to eliminate protocol skew.
3. Check client code that constructs pb.Tablet for default/zero-value strings.
4. If it recurs unexpectedly, capture the gRPC request (the error prints the Tablet via %+v) and inspect the calling component.

Example fix

// before
tablet, err := zero.ShouldServe(ctx, &pb.Tablet{GroupId: 1})

// after
tablet, err := zero.ShouldServe(ctx, &pb.Tablet{GroupId: 1, Predicate: "http://ex.com/friend"})

if tablet.Predicate == "" {
    return fmt.Errorf("cannot call ShouldServe with an empty predicate")
}

resp, err := zero.ShouldServe(ctx, tablet)
if err != nil && strings.Contains(err.Error(), "predicate is empty") {
    return fmt.Errorf("caller built an invalid Tablet message: %w", err)
}

When it happens

Trigger: Calling ShouldServe (used by alphas during tablet/oracle checks) with pb.Tablet{Predicate: ""}; buggy or misconfigured internal callers sending uninitialized Tablet structs.

Common situations: Version-skew between alpha and Zero where a field was dropped; hand-rolled clients/tests constructing Tablet messages incorrectly; corrupted internal state producing empty predicate strings.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Tablets are empty in %+v
• connection string cannot be empty
• Group ID is Zero in %+v
• Context has error: %v
• NO_ADDR: No address provided: %+v

AI-assisted analysis of dgraph-io/dgraph@759e242be6 (2026-09-01). Data as JSON: /api/errors/685e27a9fda5a3a0. Report an issue: GitHub.