apache/beam · error · UnsupportedOperationException

ReshuffleTrigger should not be used outside of Reshuffle

Error message

ReshuffleTrigger should not be used outside of Reshuffle

What it means

ReshuffleTrigger is an internal trigger that only makes sense inside the Reshuffle transform, where it is driven by the reshuffle machinery. Its getWatermarkThatGuaranteesFiring has no well-defined answer outside that context, so calling it throws UnsupportedOperationException.

Solutions

1. Do not use ReshuffleTrigger directly; use the Reshuffle transform instead
2. Replace with an explicit trigger such as AfterWatermark.pastEndOfWindow() or Repeatedly.forever(...)
3. If you need reshuffle-like behavior, use Reshuffle.viaRandomKey() rather than reimplementing its trigger

Example fix

// before
Window.into(fn).triggering(new ReshuffleTrigger<>())
// after
Window.into(fn).triggering(AfterWatermark.pastEndOfWindow())
// or apply Reshuffle.viaRandomKey() instead

if (trigger instanceof ReshuffleTrigger) throw new IllegalArgumentException("Use Reshuffle.viaRandomKey() instead of ReshuffleTrigger directly");

boolean isUserUsableTrigger(Trigger t) { return !(t instanceof ReshuffleTrigger); }

try { windowing.triggering(myTrigger); } catch (UnsupportedOperationException e) { /* fall back to AfterWatermark.pastEndOfWindow() */ }

When it happens

Trigger: Using ReshuffleTrigger directly in Window.triggering(...) or any code that calls getWatermarkThatGuaranteesFiring on a user-constructed ReshuffleTrigger.

Common situations: Developers copying Reshuffle internals to implement custom 'fire on reshuffle' semantics; reflection-based trigger inspection or serialization tests that walk all triggers.

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

• Continuation of a OnceTrigger must be a OnceTrigger
• is for internal use only and does not support case dispatch
• A function must be provided to convert the input type into…
• A PValue contained in
• A schema was provided without a data format (or viceversa)…

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/6502c589b00bd81a. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/ReshuffleTrigger.java:47

 * state.
 *
 * @param <W> The kind of window that is being reshuffled.
 */
@Internal
public class ReshuffleTrigger<W extends BoundedWindow> extends Trigger {

  public ReshuffleTrigger() {
    super();
  }

  @Override
  protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
    return this;
  }

  @Override
  public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
    throw new UnsupportedOperationException(
        "ReshuffleTrigger should not be used outside of Reshuffle");
  }

  @Override
  public boolean mayFinish() {
    return false;
  }

  @Override
  public <OutputT> OutputT accept(TriggerVisitor<OutputT> visitor) {
    return visitor.visit(this);
  }

  @Override
  public String toString() {
    return "ReshuffleTrigger()";
  }
}

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