apache/iceberg · error · UnsupportedOperationException

Count is not supported.

Error message

Count is not supported.

What it means

Counter.value() is a default method on the MetricsContext.Counter interface that throws UnsupportedOperationException('Count is not supported.') — implementations are expected to override it. A context that does not support counters (or a custom Counter implementation that skips it) leaves this stub in place, so reading the count fails.

Solutions

1. Override value() in your Counter implementation to return the real count
2. Use DefaultMetricsContext/DefaultCounter which implement value()
3. Don't read value() from counters obtained via unsupported contexts; use toString or count() where appropriate
4. Check the MetricsContext implementation actually records before consuming values

Example fix

// before
class MyCounter implements Counter<Long> { /* value() not overridden */ }
// after
class MyCounter implements Counter<Long> {
  @Override
  public Long value() { return count.get(); }
}

try { counter.value(); } catch (UnsupportedOperationException e) { skip; }

When it happens

Trigger: Calling value() on a Counter returned by a MetricsContext that did not override value(), e.g. a custom MetricsContext extending the interface without implementing counters, or the deprecated counter() default stubs on the interface.

Common situations: Custom MetricsContext implementations missing value() overrides; code reading counter values from contexts that were never meant to record (unsupported default methods); upgrade paths where a new interface method wasn't implemented.

Related errors

• Counter is not supported.
• Histogram is not supported.
• NOOP counter has no value
• NOOP timer has no count
• NOOP timer has no duration

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/5eee059e736ee42c. Report an issue: GitHub.

Appendix: source

Thrown at api/src/main/java/org/apache/iceberg/metrics/MetricsContext.java:92

    /**
     * Reporting count is optional if the counter is reporting externally.
     *
     * @return current count if available
     * @deprecated Use {@link Counter#value()}
     */
    @Deprecated
    default Optional<T> count() {
      return Optional.empty();
    }

    /**
     * Reports the current count.
     *
     * @return The current count
     */
    default T value() {
      throw new UnsupportedOperationException("Count is not supported.");
    }

    /**
     * The unit of the counter.
     *
     * @return The unit of the counter.
     */
    default Unit unit() {
      return Unit.UNDEFINED;
    }
  }

  /**
   * Get a named counter of a specific type. Metric implementations may impose restrictions on what
   * types are supported for specific counters.
   *
   * @param name name of the metric
   * @param type numeric type of the counter value

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