apache/druid · error · java.lang.UnsupportedOperationException

ApproximateHistogramFoldingBufferAggregator does not…

Error message

ApproximateHistogramFoldingBufferAggregator does not support getLong()

What it means

ApproximateHistogramFoldingBufferAggregator.getLong() is deliberately unimplemented: the buffered aggregation produces an ApproximateHistogram, and no long representation exists. The method throws UnsupportedOperationException unconditionally when invoked.

Solutions

Extract numbers via histogram post-aggregators (quantile, min, max) rather than getLong().
Use a long-capable aggregator (longSum, longMax) on the raw column when a long result is needed.
In generic code, check aggregator output type or catch UnsupportedOperationException and fall back to histogram object access.

Example fix

// before
long v = bufferAggregator.getLong(buf, position);
// after
// query JSON:
// {"type": "min", "fieldName": "histFold"}
long v = (long) minPostAggResult;

Defensive patterns

Strategy: validation

Validate before calling

// Verify long support before buffered accessor call:
boolean isFoldBuffer = aggregator instanceof org.apache.druid.query.aggregation.histogram.ApproximateHistogramFoldingBufferAggregator;
if (!isFoldBuffer) { value = aggregator.getLong(buf, position); }

Type guard

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

Try / catch

try {
  value = aggregator.getLong(buf, position);
} catch (UnsupportedOperationException e) {
  value = (long) maxFromHistogramBuffer(buf, position);
}

Prevention

Do not call getLong on histogram folding buffer aggregators; it is unsupported by design.
Use long-capable aggregators when long output is required.
Keep a mapping of aggregator types to supported accessor methods in custom query engines.

When it happens

Trigger: Calling ApproximateHistogramFoldingBufferAggregator.getLong(ByteBuffer, int), or queries whose result extraction path invokes getLong on a buffer-aggregated approxHistogramFold column.

Common situations: Engine code assuming every BufferAggregator implements getLong; queries mixing histogram folds with long-typed metric expectations; custom post-processing that reads raw aggregation buffers numerically.

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/d265d48898c73b22. Report an issue: GitHub.

Appendix: source

Thrown at extensions-core/histogram/src/main/java/org/apache/druid/query/aggregation/histogram/ApproximateHistogramFoldingBufferAggregator.java:72

    innerAggregator.aggregate(buf, position, hNext);
  }

  @Override
  public Object get(ByteBuffer buf, int position)
  {
    return innerAggregator.get(buf, position);
  }

  @Override
  public float getFloat(ByteBuffer buf, int position)
  {
    throw new UnsupportedOperationException("ApproximateHistogramFoldingBufferAggregator does not support getFloat()");
  }

  @Override
  public long getLong(ByteBuffer buf, int position)
  {
    throw new UnsupportedOperationException("ApproximateHistogramFoldingBufferAggregator does not support getLong()");
  }

  @Override
  public double getDouble(ByteBuffer buf, int position)
  {
    throw new UnsupportedOperationException("ApproximateHistogramFoldingBufferAggregator does not support getDouble()");
  }

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

  @Override
  public void inspectRuntimeShape(RuntimeShapeInspector inspector)
  {
    inspector.visit("selector", selector);

View on GitHub (pinned to 9b90983fd2)