apache/druid · error · java.lang.UnsupportedOperationException

CardinalityBufferAggregator does not support getFloat()

Error message

CardinalityBufferAggregator does not support getFloat()

What it means

CardinalityBufferAggregator aggregates HLL sketches into a ByteBuffer and only supports reading the sketch via get(). getFloat() throws UnsupportedOperationException because no float primitive is stored.

Source

Thrown at processing/src/main/java/org/apache/druid/query/aggregation/cardinality/CardinalityBufferAggregator.java:85

        CardinalityAggregator.hashValues(selectorPluses, collector);
      }
    }
    finally {
      buf.limit(oldLimit);
      buf.position(oldPosition);
    }
  }

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

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


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

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

  @Override
  public void close()
  {

View on GitHub (pinned to 9b90983fd2)

Solutions

Read the sketch via get(buf, position) (HyperUniquesBufferAggregator.doGet) instead of getFloat()
Use the cardinality aggregation only with object/string-typed result handling
Choose a numeric aggregator if a float result is required

Example fix

// before
float v = bufferAggregator.getFloat(buf, position);
// after
Object v = bufferAggregator.get(buf, position); // HLL sketch

Defensive patterns

Strategy: type-guard

Validate before calling

if (!(aggFactory instanceof CardinalityAggregatorFactory)) { float v = bufferAggregator.getFloat(buf, position); }

Type guard

if (factory instanceof CardinalityAggregatorFactory) {
    Object v = bufferAggregator.get(buf, position);
} else {
    float v = bufferAggregator.getFloat(buf, position);
}

Try / catch

try {
    v = bufferAggregator.getFloat(buf, position);
} catch (UnsupportedOperationException e) {
    v = Float.NaN;
}

Prevention

Read cardinality buffer results via get()/HyperUniquesBufferAggregator.doGet
Avoid numeric-typed result extraction for cardinality aggregations
Match aggregation factory type to result-row column type

When it happens

Trigger: Calling bufferAggregator.getFloat(buf, position) on a CardinalityAggregatorFactory-created buffer aggregator, i.e. when the query engine resolves the aggregation type as FLOAT.

Common situations: Vectorized/numeric result extraction on a cardinality aggregation; custom code assuming all buffer aggregators expose numeric getters.

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/a981fa42edd28321. Report an issue: GitHub.