VictoriaMetrics/VictoriaMetrics · error

cannot read sum

Error message

cannot read sum

What it means

Case 6 (field 'sum', double) failed: fc.Double() returned ok=false so the parser cannot extract the sum value from the wire. As with the other numeric fields, malformed wire data causes an immediate abort of the whole Sketch message.

Source

Thrown at lib/protoparser/datadogsketches/parser.go:294

				return fmt.Errorf("cannot read count")
			}
			d.Cnt = cnt
		case 3:
			v, ok := fc.Double()
			if !ok {
				return fmt.Errorf("cannot read min")
			}
			d.Min = v
		case 4:
			v, ok := fc.Double()
			if !ok {
				return fmt.Errorf("cannot read max")
			}
			d.Max = v
		case 6:
			sum, ok := fc.Double()
			if !ok {
				return fmt.Errorf("cannot read sum")
			}
			d.Sum = sum
		case 7:
			var ok bool
			d.K, ok = fc.UnpackSint32s(d.K)
			if !ok {
				return fmt.Errorf("cannot read k")
			}
		case 8:
			var ok bool
			d.N, ok = fc.UnpackUint32s(d.N)
			if !ok {
				return fmt.Errorf("cannot read n")
			}
		}
	}
	return nil
}

View on GitHub (pinned to 5079fb58f1)

Solutions

1. Verify the payload with protoc --decode using the datadog agent proto definitions
2. Correct the client serializer so sum is a double (wire type 1, 8 bytes)
3. Test with the official Datadog agent pointed at the VM endpoint to isolate sender bugs
4. Update VictoriaMetrics to the latest version

// Validate sum is 8-byte fixed64 double in the payload before sending
buf := new(bytes.Buffer)
binary.Write(buf, binary.LittleEndian, math.Float64bits(sum)) // reference encoding

if err := stream.Parse(r, callback); err != nil {
    if strings.Contains(err.Error(), "cannot read sum") { /* fix encoder */ }
}

When it happens

Trigger: Sketch payload where field 6 is truncated or encoded with a non-fixed64 wire type, e.g. by a client that serializes sum incorrectly.

Common situations: Custom exporters hand-encoding the Dogsketches protobuf, corrupted traffic through gateways, or mixing protocol versions between sender and VM.

Understand the failure class

Background: "cannot parse invalid wire-format data", "cannot unmarshal", "failed unmarshalling": protobuf unmarshal errors explained — this error's family across 10 libraries.

Related errors

• cannot read count
• cannot read min
• cannot read max
• cannot read Sketch data
• cannot unmarshal Sketch: %w

AI-assisted analysis of VictoriaMetrics/VictoriaMetrics@5079fb58f1 (2026-09-03). Data as JSON: /api/errors/983d036564d8d29b. Report an issue: GitHub.