What causes "error decoding double field" in apache/beam?

Verify input completeness and encoder compatibility.

error decoding double field

Error message

error decoding double field

What it means

Wrap added by reflectDecodeFloat when DecodeDouble fails reading an 8-byte double from the element stream. The cause is EOF/truncated row bytes or corrupt data for a float64 field — typically a producer/consumer coder mismatch or damaged intermediate data.

Solutions

Verify input completeness and encoder compatibility.
Re-encode the source data with the current coder.
Ensure schema evolution compatibility between writer and reader.
Inspect raw bytes at the failure point for corruption.

Defensive patterns

Strategy: try-catch

Try / catch

if err := decoderFn(rv, r); err != nil {
    if strings.Contains(err.Error(), "error decoding double field") {
        return fmt.Errorf("truncated float64 field in row: %w", err)
    }
    return err
}

Prevention

Verify each record has room for all 8-byte doubles before decoding.
Keep float field types consistent between schema versions.
Detect truncation (io.EOF) upstream and surface record offsets.
Test decoding of persisted fixtures after any struct change.

When it happens

Trigger: reflectDecodeFloat during row decoding when DecodeDouble cannot read 8 bytes — truncated stream or misaligned field decode of incompatible data.

Common situations: Reading partially-written outputs, mixing pipeline versions with different row schemas, decoding foreign byte blobs.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/733bc0a9389d8b7e. Report an issue: GitHub.

Appendix: source

Thrown at sdks/go/pkg/beam/core/graph/coder/row_decoder.go:256

		return errors.Wrap(err, "error decoding varint field")
	}
	rv.SetUint(v)
	return nil
}

func reflectDecodeSinglePrecisionFloat(rv reflect.Value, r io.Reader) error {
	v, err := DecodeSinglePrecisionFloat(r)
	if err != nil {
		return errors.Wrap(err, "error decoding single-precision float field")
	}
	rv.SetFloat(float64(v))
	return nil
}

func reflectDecodeFloat(rv reflect.Value, r io.Reader) error {
	v, err := DecodeDouble(r)
	if err != nil {
		return errors.Wrap(err, "error decoding double field")
	}
	rv.SetFloat(v)
	return nil
}

func reflectDecodeByteSlice(rv reflect.Value, r io.Reader) error {
	b, err := DecodeBytes(r)
	if err != nil {
		return errors.Wrap(err, "error decoding []byte field")
	}
	rv.SetBytes(b)
	return nil
}

// customFunc returns nil if no custom func exists for this type.
// If an error is returned, coder construction should be aborted.
func (b *RowDecoderBuilder) customFunc(t reflect.Type) (func(io.Reader) (any, error), bool, error) {
	if fact, ok := b.allFuncs[t]; ok {

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