VictoriaMetrics/VictoriaMetrics · error

cannot read count_float

Error message

cannot read count_float

What it means

Field 2 of the Histogram message is sum as double. unmarshalHistogram calls fc.Double(); if the bytes cannot be read as a fixed64 double it returns "cannot read count_float". Note the message text says count_float but the failing field here is the sum (field 3 path shown); the cause is a wrong wire type or corrupt fixed64 bytes.

Source

Thrown at lib/prompb/write_request_unmarshaler.go:261

	var err error
	var fc easyproto.FieldContext
	for len(src) > 0 {
		src, err = fc.NextField(src)
		if err != nil {
			return tss, labelsPool, samplesPool, fmt.Errorf("cannot read next field: %w", err)
		}
		var ok bool
		switch fc.FieldNum {
		case 1:
			nhctx.countInt, ok = fc.Uint64()
			if !ok {
				return tss, labelsPool, samplesPool, fmt.Errorf("cannot read count_int")
			}
		case 2:
			nhctx.countFloat, ok = fc.Double()
			if !ok {
				return tss, labelsPool, samplesPool, fmt.Errorf("cannot read count_float")
			}
			nhctx.isCountFloat = true
		case 3:
			nhctx.sum, ok = fc.Double()
			if !ok {
				return tss, labelsPool, samplesPool, fmt.Errorf("cannot read sum")
			}
		case 4:
			nhctx.schema, ok = fc.Sint32()
			if !ok {
				return tss, labelsPool, samplesPool, fmt.Errorf("cannot read schema")
			}
		case 5:
			nhctx.zeroThreshold, ok = fc.Double()
			if !ok {
				return tss, labelsPool, samplesPool, fmt.Errorf("cannot read zero_threshold")
			}
		case 6:

View on GitHub (pinned to 5079fb58f1)

Solutions

1. Verify count_float (field 2) and sum (field 3) are both encoded as wire type 1 fixed64 doubles
2. Check for truncation — an 8-byte double cut short by a bad length prefix produces exactly this failure
3. Regenerate the client from the canonical prompb proto and retest
4. Round-trip the payload through a reference decoder (protoc --decode) to locate the malformed field

Example fix

// before: sum encoded as varint
hb = protowire.AppendTag(hb, 3, protowire.VarintType)
hb = protowire.AppendVarint(hb, uint64(sum))
// after: sum encoded as fixed64 double
hb = protowire.AppendTag(hb, 3, protowire.Fixed64Type)
hb = protowire.AppendFixed64(hb, math.Float64bits(sum))

func validateDoubleField(data []byte) bool {
    _, n := protowire.ConsumeFixed64(data)
    return n > 0
}

if err := unmarshalHistogram(data, tss, lp, sp, labels, fb); err != nil {
    if strings.Contains(err.Error(), "cannot read count_float") || strings.Contains(err.Error(), "cannot read sum") {
        log.Printf("bad double field in histogram: %v", err)
        return errBadHistogramField
    }
    return err
}

When it happens

Trigger: UnmarshalProtobuf processes a Histogram whose field 2 (count_float) or field 3 (sum) bytes are not valid 8-byte fixed64 doubles — e.g. count_float encoded as varint, or sum truncated to fewer than 8 bytes.

Common situations: Custom histogram serializers using varints for float fields; truncated messages cutting a double in half; clients built against drifted proto definitions where field numbers shifted.

Related errors

• cannot read native histogram data
• failed to unmarshal native histogram: %w
• cannot read count_int
• cannot read label data
• cannot unmarshal label: %w

AI-assisted analysis of VictoriaMetrics/VictoriaMetrics@5079fb58f1 (2026-09-03). Data as JSON: /api/errors/4fe12d87deab43f5. Report an issue: GitHub.