What causes "Not implemented" in apache/druid?

Use get() to obtain the ArrayOfDoublesSketch object instead of getLong()/getFloat()

apache/druid · error · java.lang.UnsupportedOperationException

Not implemented

Error message

Not implemented

What it means

ArrayOfDoublesSketchBuildAggregator aggregates into an ArrayOfDoublesSketch complex object, so numeric accessors like getLong() (and getFloat()) have no meaningful value to return; they unconditionally throw UnsupportedOperationException. This surfaces if a query or metric extraction asks for the aggregation result as a long/float primitive.

Solutions

Use get() to obtain the ArrayOfDoublesSketch object instead of getLong()/getFloat()
Use the tuple-sketch specific post-aggregators (e.g. ArrayOfDoublesSketchTo Estimates/sums) to extract numeric results
In SQL, wrap with the appropriate tuple sketch functions (e.g. DS_DOUBLES_* estimators) rather than casting the sketch to a number

Example fix

// before
long v = aggregator.getLong(); // throws
// after
ArrayOfDoublesSketch sketch = (ArrayOfDoublesSketch) aggregator.get();
double estimate = sketch.getEstimate();

Defensive patterns

Strategy: validation

Validate before calling

if (aggregator instanceof ArrayOfDoublesSketchBuildAggregator) {
  Object result = ((ArrayOfDoublesSketchBuildAggregator) aggregator).get(); // use get(), never getLong()
}

Type guard

boolean yieldsNumeric(ArrayOfDoublesSketchBuildAggregator agg) {
  return false; // numeric accessors are unsupported; always use get()
}

Try / catch

try {
  long v = aggregator.getLong();
} catch (UnsupportedOperationException e) {
  ArrayOfDoublesSketch s = (ArrayOfDoublesSketch) aggregator.get();
  // extract estimates via tuple sketch post-aggregators
}

Prevention

Never use numeric getters on sketch aggregators; call get()
Use tuple-sketch specific post-aggregators for numeric results
In SQL, use DS_DOUBLES_* functions instead of casting sketch columns to numbers

When it happens

Trigger: Querying an ArrayOfDoublesSketch aggregator column with a numeric accessor — e.g. selecting the raw aggregator output in a context that calls getLong()/getFloat(), or configuring a post-aggregator that reads the sketch value as a number instead of using the tuple sketch specific post-aggregators.

Common situations: Using SUM/MIN/MAX or other numeric aggregators directly on the tuple sketch column; selecting the sketch column in SQL where the planner requests a primitive; writing custom code that calls getLong() on the aggregator instead of get() to fetch the sketch object.

Related errors

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/118d1804ed902223. Report an issue: GitHub.

Appendix: source

Thrown at extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/tuple/ArrayOfDoublesSketchBuildAggregator.java:149

  /**
   * This method uses synchronization because it can be used during indexing,
   * and Druid can call aggregate() and get() concurrently
   * https://github.com/apache/druid/pull/3956
   * The returned sketch is a separate instance of ArrayOfDoublesCompactSketch
   * representing the current state of the aggregation, and is not affected by consequent
   * aggregate() calls
   */
  @Override
  public synchronized Object get()
  {
    initializeSketchIfNeeded();
    return sketch.compact();
  }

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

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

  @Override
  public void close()
  {
    sketch = null;
    values = null;
  }

  /**
   * Initialize {@link #sketch} if it is null.
   */

View on GitHub (pinned to 9b90983fd2)