apache/druid · error · UnsupportedOperationException

Not implemented

Error message

Not implemented

What it means

DoublesSketchMergeAggregator unions existing quantiles DoublesSketches; the result is a sketch, not a scalar, so getFloat() deliberately throws UnsupportedOperationException. Numeric access to a merge aggregator is not supported by design.

Source

Thrown at extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchMergeAggregator.java:58

  }

  @Override
  public synchronized void aggregate()
  {
    updateUnion(selector, union);
  }


  @Override
  public synchronized Object get()
  {
    return union.getResult();
  }

  @Override
  public float getFloat()
  {
    throw new UnsupportedOperationException("Not implemented");
  }

  @Override
  public long getLong()
  {
    throw new UnsupportedOperationException("Not implemented");
  }

  @Override
  public synchronized void close()
  {
    union = null;
  }

  static void updateUnion(ColumnValueSelector selector, DoublesUnion union)
  {
    final Object object = selector.getObject();
    if (object == null) {

View on GitHub (pinned to 9b90983fd2)

Solutions

  1. Call get() which returns union.getResult() (the sketch) or the finalized value
  2. Set shouldFinalize=true and read via get() when a numeric quantile/rank is needed
  3. Use quantilesDoublesSketchToQuantile/ToRank post-aggregators for typed numeric output

Example fix

// before
float v = mergeAggregator.getFloat();
// after
Object result = mergeAggregator.get();
double v = ((Number) result).doubleValue(); // when shouldFinalize=true
Defensive patterns

Strategy: type-guard

Validate before calling

Object result = mergeAggregator.get();
if (!(result instanceof DoublesSketch) && !(result instanceof Number)) {
  throw new IllegalStateException("Unexpected merged sketch result: " + (result == null ? "null" : result.getClass()));
}

Type guard

boolean isFinalized(Aggregator agg) { return agg.get() instanceof Number; }

Try / catch

try {
  return mergeAggregator.getFloat();
} catch (UnsupportedOperationException e) {
  Object v = mergeAggregator.get();
  return v instanceof Number ? ((Number) v).floatValue() : Float.NaN;
}

Prevention

When it happens

Trigger: Calling getFloat() on a DoublesSketchMergeAggregator, e.g. when a query or custom code path expects a float output from a merging quantilesDoublesSketch aggregation.

Common situations: Merging sketches in subqueries whose results are consumed by numeric selectors; generic aggregator code paths defaulting to getFloat; tests asserting numeric merging.

Related errors

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/7087403dd7d4c0b7. Report an issue: GitHub.