apache/druid · error · UnsupportedOperationException

HistogramBufferAggregator does not support getFloat()

Error message

HistogramBufferAggregator does not support getFloat()

What it means

HistogramBufferAggregator is the off-heap (ByteBuffer-based) variant of the histogram aggregator in Druid. Its getFloat() is intentionally unimplemented: a histogram aggregate cannot be represented as a single float, so the method throws UnsupportedOperationException. The error indicates the query framework attempted float-valued access on a histogram metric.

Source

Thrown at processing/src/main/java/org/apache/druid/query/aggregation/HistogramBufferAggregator.java:93

  }

  @Override
  public Object get(ByteBuffer buf, int position)
  {
    long[] bins = new long[breaks.length + 1];
    ByteBuffer mutationBuffer = buf.duplicate();
    mutationBuffer.position(position);
    mutationBuffer.asLongBuffer().get(bins);

    float min = mutationBuffer.getFloat(position + minOffset);
    float max = mutationBuffer.getFloat(position + maxOffset);
    return new Histogram(breaks, bins, min, max);
  }

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

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

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

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

View on GitHub (pinned to 9b90983fd2)

Solutions

Retrieve the histogram result via get(ByteBuffer, int), which returns the Histogram object.
Use a float-producing aggregator (floatSum, doubleSum) instead of histogram when a FLOAT output is needed.
Remove FLOAT coercion/post-aggregators from the histogram metric in the query spec.
If histogram statistics are needed, finalize the histogram and aggregate over its bins downstream.

Example fix

// before
float f = bufferAgg.getFloat(buf, position); // throws
// after
Object val = bufferAgg.get(buf, position);
Histogram hist = (Histogram) val;

Defensive patterns

Strategy: type-guard

Validate before calling

if (bufferAggregator instanceof HistogramBufferAggregator) {
  // must use get(buf, position); never call getFloat()
}

Type guard

boolean supportsFloat(BufferAggregator agg) {
  return !(agg instanceof HistogramBufferAggregator);
}

Try / catch

try {
  value = agg.getFloat(buf, position);
} catch (UnsupportedOperationException e) {
  Object h = agg.get(buf, position);
}

Prevention

Branch on aggregator type before calling primitive getters on buffer aggregators
Keep FLOAT post-aggregators away from histogram metrics
Validate the query spec's metric types at plan time
Use get(ByteBuffer,int) for object-typed aggregators

When it happens

Trigger: A native query using a 'histogram' aggregator is executed in a buffer-based engine path (groupBy/older timeseries) where the metric is retrieved via BufferAggregator.getFloat(); e.g. a float-typed post-aggregator or FLOAT coercion applied to the histogram column.

Common situations: FLOAT-typed SQL aggregation over a histogram column; post-aggregator chains that default to float accessors; custom engine code calling getFloat() on buffer aggregators without checking the aggregator type; queries written for numeric aggregators retargeted to histogram.

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/5d3cfdc557885f76. Report an issue: GitHub.