apache/beam · error · UnsupportedOperationException

Cannot outputWindowedValue from TruncateRestriction

Error message

Cannot outputWindowedValue from TruncateRestriction

What it means

Same contract as the timestamp variant: the OutputReceiver handed to @TruncateRestriction cannot emit windowed values at all. outputWindowedValue throws UnsupportedOperationException because truncation may only yield restrictions, never elements.

Solutions

1. Remove the outputWindowedValue call from @TruncateRestriction.
2. Restrict all element/windowed output to @ProcessElement.
3. Use a WindowedOutputReceiver only where the runner supplies one (processElement context).

Example fix

// before
@TruncateRestriction void truncate(Restriction r, WindowedOutputReceiver<Restriction> out) { out.outputWindowedValue(r, now, windows, pane); }
// after
@TruncateRestriction void truncate(Restriction r, OutputReceiver<Restriction> out) { /* no element output */ }

boolean isTruncateReceiver = receiver instanceof SplittableTruncateSizedRestrictionsDoFnRunner.TruncateRestrictionReceiver; // no windowed output if true

try { out.outputWindowedValue(r, ts, windows, pane); } catch (UnsupportedOperationException e) { LOG.error("Windowed output unsupported in truncateRestriction"); }

When it happens

Trigger: Calling outputWindowedValue(...) (with windows/pane args) on the receiver available inside a @TruncateRestriction method.

Common situations: Trying to emit to multiple windows or with a custom pane during truncation; porting code that used a full OutputReceiver/WindowedOutputReceiver into truncateRestriction.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Cannot outputWithTimestamp from SplitRestriction
• Cannot outputWithTimestamp from TruncateRestriction
• RecordId unsupported in
• RecordOffset unsupported in
• Restriction unsupported in

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/a4dc3832ef19c121. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/harness/src/main/java/org/apache/beam/fn/harness/SplittableTruncateSizedRestrictionsDoFnRunner.java:935

    @Override
    public PipelineOptions pipelineOptions() {
      return pipelineOptions;
    }

    @Override
    public void outputWithTimestamp(RestrictionT output, Instant timestamp) {
      throw new UnsupportedOperationException(
          "Cannot outputWithTimestamp from TruncateRestriction");
    }

    @Override
    public void outputWindowedValue(
        RestrictionT output,
        Instant timestamp,
        Collection<? extends BoundedWindow> windows,
        PaneInfo paneInfo) {
      throw new UnsupportedOperationException(
          "Cannot outputWindowedValue from TruncateRestriction");
    }
  }

  /**
   * Passes split requests downstream, by way of trySplit on the overall runner, which will split
   * per window if needed.
   */
  private static class SplitDelegatingFnDataReceiver<
          InputT, RestrictionT extends @NonNull Object, WatermarkEstimatorStateT>
      implements FnDataReceiver<
              WindowedValue<KV<KV<InputT, KV<RestrictionT, WatermarkEstimatorStateT>>, Double>>>,
          HandlesSplits {

    private final HandlesSplits splitDelegate;
    private final SplittableTruncateSizedRestrictionsDoFnRunner<
            InputT, RestrictionT, ?, WatermarkEstimatorStateT, ?>
        runner;

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