apache/druid · error · java.lang.UnsupportedOperationException

ApproximateHistogramFoldingAggregator does not support getLo

Error message

ApproximateHistogramFoldingAggregator does not support getLong()

What it means

ApproximateHistogramFoldingAggregator.getLong() throws UnsupportedOperationException by design: the folded result is an ApproximateHistogram object and no long representation is defined. Any attempt to read the aggregation as a long fails.

Source

Thrown at extensions-core/histogram/src/main/java/org/apache/druid/query/aggregation/histogram/ApproximateHistogramFoldingAggregator.java:78

    }
  }

  @Override
  public Object get()
  {
    return histogram;
  }

  @Override
  public float getFloat()
  {
    throw new UnsupportedOperationException("ApproximateHistogramFoldingAggregator does not support getFloat()");
  }

  @Override
  public long getLong()
  {
    throw new UnsupportedOperationException("ApproximateHistogramFoldingAggregator does not support getLong()");
  }

  @Override
  public double getDouble()
  {
    throw new UnsupportedOperationException("ApproximateHistogramFoldingAggregator does not support getDouble()");
  }

  @Override
  public void close()
  {
    // no resources to cleanup
  }
}

View on GitHub (pinned to 9b90983fd2)

Solutions

Derive numbers with histogram post-aggregators (quantile, min, max) instead of getLong().
Use a long-capable aggregator (e.g. longSum) on the raw column when a long is required.
Add a capability check or try/catch around getLong() in generic code paths.

Example fix

// before
long v = foldingAggregator.getLong();
// after
// use post-aggregation in the query:
// {"type": "max", "fieldName": "histFold"}
long v = (long) maxPostAggResult;

Defensive patterns

Strategy: validation

Validate before calling

// Check type before getLong:
boolean isFoldAgg = aggregator instanceof org.apache.druid.query.aggregation.histogram.ApproximateHistogramFoldingAggregator;
if (!isFoldAgg) { value = aggregator.getLong(); }

Type guard

boolean supportsLong(Object agg) {
  return !(agg instanceof org.apache.druid.query.aggregation.histogram.ApproximateHistogramFoldingAggregator);
}

Try / catch

try {
  value = aggregator.getLong();
} catch (UnsupportedOperationException e) {
  value = (long) histogramMax(aggregator.get());
}

Prevention

Use longSum/longMax for long outputs; reserve approxHistogramFold for histogram analytics.
Never assume getLong() exists on every Aggregator implementation.
Add unit coverage for query plans that combine histogram folds with numeric accessors.

When it happens

Trigger: Calling ApproximateHistogramFoldingAggregator.getLong(), or queries that treat approxHistogramFold output as a long-typed metric.

Common situations: Framework code assuming getLong() exists on all aggregators; queries mixing histogram folds with long metric accessors; custom extensions extracting values from aggregator results generically.

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

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/761a713bb67cd4c6. Report an issue: GitHub.