apache/beam · error · IllegalArgumentException

Unknown accumulation mode [${accumulationMode}]

Error message

Unknown accumulation mode [${accumulationMode}]

What it means

WindowBuilder.accumulationMode() maps an AccumulationMode enum to the corresponding Beam windowing behavior (discarding/accumulating fired panes). An unrecognized mode hits the default branch and throws IllegalArgumentException listing the unsupported mode.

Source

Thrown at sdks/java/extensions/euphoria/src/main/java/org/apache/beam/sdk/extensions/euphoria/core/client/operator/WindowBuilder.java:93

  }

  @Override
  public WindowBuilder<T> triggeredBy(Trigger trigger) {
    window = requireNonNull(window).triggering(trigger);
    return this;
  }

  @Override
  public WindowBuilder<T> accumulationMode(WindowingStrategy.AccumulationMode accumulationMode) {
    switch (requireNonNull(accumulationMode)) {
      case DISCARDING_FIRED_PANES:
        window = requireNonNull(window).discardingFiredPanes();
        break;
      case ACCUMULATING_FIRED_PANES:
        window = requireNonNull(window).accumulatingFiredPanes();
        break;
      default:
        throw new IllegalArgumentException("Unknown accumulation mode [" + accumulationMode + "]");
    }
    return this;
  }

  @Override
  public WindowBuilder<T> withAllowedLateness(Duration allowedLateness) {
    window = requireNonNull(window).withAllowedLateness(requireNonNull(allowedLateness));
    return this;
  }

  @Override
  public WindowBuilder<T> withAllowedLateness(
      Duration allowedLateness, Window.ClosingBehavior closingBehavior) {
    window =
        requireNonNull(window)
            .withAllowedLateness(requireNonNull(allowedLateness), requireNonNull(closingBehavior));
    return this;
  }

View on GitHub (pinned to 12126d8942)

Solutions

1. Use only accumulation modes supported by the builder (e.g. ACCUMULATING_FIRED_PANES or the default discarding behavior).
2. Check the euphoria extension source for the exact set of handled modes at your Beam version.
3. Upgrade or patch the euphoria extension if a newly added AccumulationMode constant is required.

Example fix

// before
builder.accumulationMode(AccumulationMode.RETRACTING_FIRED_PANES);
// after
builder.accumulationMode(AccumulationMode.ACCUMULATING_FIRED_PANES);

if (mode != AccumulationMode.DISCARDING_FIRED_PANES
    && mode != AccumulationMode.ACCUMULATING_FIRED_PANES) {
  throw new IllegalArgumentException("Unsupported accumulation mode: " + mode);
}

try {
  builder.accumulationMode(mode);
} catch (IllegalArgumentException e) {
  builder.accumulationMode(AccumulationMode.ACCUMULATING_FIRED_PANES);
}

When it happens

Trigger: Calling windowBuilder.accumulationMode(AccumulationMode.X) with a mode not handled by the switch (the code handles DISCARDING_FIRED_PANES, ACCUMULATING_FIRED_PANES, and possibly others; e.g. RETRACTING or UNSPECIFIED-style values fall through), typically inside a Window.into(...).triggering(...).accumulationMode(...) chain.

Common situations: Upgrading Beam where AccumulationMode gained new constants while the euphoria WindowBuilder switch wasn't extended; typos/mismatches when porting Flink-style accumulation settings to Beam euphoria.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• Unknown policy ${policy}
• Cannot convert unknown %s to %s: %s
• Unknown failure mode + failureMode
• Unrecognized value for stable unique names:
• Cannot encode null window

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/87c8ea328eb85960. Report an issue: GitHub.