{"record":{"id":"a0dc53361743e2e6","repo":"apache/beam","slug":"error-writing-state-v","errorCode":null,"errorMessage":"error writing state: %v","messagePattern":"error writing state: (.+?)","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"sdks/go/pkg/beam/io/fileio/match.go","lineNumber":387,"sourceCode":"type dedupFn struct {\n\tState state.Value[struct{}]\n}\n\nfunc (fn *dedupFn) ProcessElement(\n\tsp state.Provider,\n\t_ string,\n\tmd FileMetadata,\n\temit func(FileMetadata),\n) error {\n\t_, ok, err := fn.State.Read(sp)\n\tif err != nil {\n\t\treturn fmt.Errorf(\"error reading state: %v\", err)\n\t}\n\n\tif !ok {\n\t\temit(md)\n\t\tif err := fn.State.Write(sp, struct{}{}); err != nil {\n\t\t\treturn fmt.Errorf(\"error writing state: %v\", err)\n\t\t}\n\t}\n\n\treturn nil\n}\n\ntype dedupUnmodifiedFn struct {\n\tState state.Value[int64]\n}\n\nfunc (fn *dedupUnmodifiedFn) ProcessElement(\n\tsp state.Provider,\n\t_ string,\n\tmd FileMetadata,\n\temit func(FileMetadata),\n) error {\n\tprevMTime, ok, err := fn.State.Read(sp)\n\tif err != nil {","sourceCodeStart":369,"sourceCodeEnd":405,"githubUrl":"https://github.com/apache/beam/blob/12126d8942aaf848030c478b4c6a28c6af861c66/sdks/go/pkg/beam/io/fileio/match.go#L369-L405","documentation":"This error is returned by the stateful match DoFn in Apache Beam's fileio package when writing to its persistent State API fails. After a file's metadata is emitted because no prior state entry existed, the DoFn records a sentinel in its BagState/ValueState; if the state write fails (typically a runner or backing store failure), the raw error is wrapped with this message and the bundle fails.","triggerScenarios":"Calling ProcessElement on a first-seen file (State.Read returned ok=false) where fn.State.Write(sp, struct{}{}) fails, e.g. due to runner state-store outage, serialization issues, or a state backend error.","commonSituations":"Runner-side state storage failures (e.g. Flink/Spark state backend or Dataflow streaming engine hiccups), OOM or disk issues in the state backend, or using state in a context where the runner does not fully support it.","solutions":["Retry the pipeline/bundle; state write failures are usually transient backend issues.","Check the wrapped inner error (%v) to identify the underlying state backend failure.","Verify the runner supports the Beam State API and that the state backend is healthy and sized correctly.","Upgrade the SDK/runner if the inner error points to a known state serialization bug."],"exampleFix":"// before\nif err := fn.State.Write(sp, struct{}{}); err != nil {\n\treturn fmt.Errorf(\"error writing state: %v\", err)\n}\n// after\nif err := fn.State.Write(sp, struct{}{}); err != nil {\n\treturn fmt.Errorf(\"error writing state for key %v: %w\", sp, err) // preserve cause with %w for errors.Is/As","handlingStrategy":"try-catch","validationCode":"// Go: no pre-call check possible; verify runner state support up front\nif !runnerSupportsStateAPI() { return errors.New(\"runner does not support Beam State API\") }","typeGuard":null,"tryCatchPattern":"if err := ProcessElement(...); err != nil {\n\tvar wrapped = err.Error()\n\tif strings.Contains(wrapped, \"error writing state\") {\n\t\t// inspect inner cause, retry bundle / alert on state backend\n\t}\n}","preventionTips":["Monitor state backend health (checkpoints, storage errors) for streaming jobs.","Keep the runner and SDK versions compatible with the State API.","Add retry/idempotency at the pipeline level since DoFn errors fail bundles.","Log the inner error, not just the wrapper, for faster diagnosis."],"tags":["go","apache-beam","state-api","dofn"],"backgroundTag":"file-write-failed","analyzedSha":"12126d8942aaf848030c478b4c6a28c6af861c66","analyzedAt":"2026-09-13T01:50:10.254Z","contentChangedAt":"2026-09-13T01:50:10.254Z","schemaVersion":2},"datasetVersion":"2026-09-14T16:17:12.679Z"}