apache/beam · error

error reading state

Error message

error reading state: %v

What it means

In fileio's matched-file filter DoFn, ProcessElement reads the pipeline State cell (fn.State.Read(sp)) that tracks which files were already emitted. If the state read itself fails (as opposed to returning ok=false), the error is wrapped with this message. This is a state-management/runtime failure, not a file problem.

Solutions

1. Check the wrapped %v error and the runner's state backend health/logs (Flink checkpoints, Dataflow state service)
2. Verify the runner supports the Beam state API and that the state cell type hasn't changed between job versions
3. Retry the pipeline after restoring backend availability; transient read failures usually resolve
4. If state is unnecessary for your use case, run MatchAll without the dedup/filter step to avoid the state dependency

_, ok, err := fn.State.Read(sp)
if err != nil {
	if isTransient(err) { return retryRead(sp) }
	return fmt.Errorf("state read failed: %w", err)
}

When it happens

Trigger: fn.State.Read(sp) returns a non-nil err in ProcessElement (match.go:381): the runner's state backend (e.g. Flink/Kafka/state API) is unavailable, the state cell is corrupted, or the state bag fails to decode.

Common situations: Runner state backend outage or misconfiguration; using a runner that lacks full state API support; state bag type incompatibility after upgrading the pipeline code under an existing job/state store.

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

• A cannot be expanded
• Attempting to add message
• can't get data to render
• Cannot access state in non-window observing context.
• computeFacts: unable to check

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/00a9fc0588763fde. Report an issue: GitHub.

Appendix: source

Thrown at sdks/go/pkg/beam/io/fileio/match.go:381

}

func keyByPath(md FileMetadata) (string, FileMetadata) {
	return md.Path, md
}

type dedupFn struct {
	State state.Value[struct{}]
}

func (fn *dedupFn) ProcessElement(
	sp state.Provider,
	_ string,
	md FileMetadata,
	emit func(FileMetadata),
) error {
	_, ok, err := fn.State.Read(sp)
	if err != nil {
		return fmt.Errorf("error reading state: %v", err)
	}

	if !ok {
		emit(md)
		if err := fn.State.Write(sp, struct{}{}); err != nil {
			return fmt.Errorf("error writing state: %v", err)
		}
	}

	return nil
}

type dedupUnmodifiedFn struct {
	State state.Value[int64]
}

func (fn *dedupUnmodifiedFn) ProcessElement(
	sp state.Provider,

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