apache/druid · error · IllegalArgumentException

Must have a valid, non-null aggregator name

Error message

Must have a valid, non-null aggregator name

What it means

DoublesSketchAggregatorFactory (Apache Druid datasketches quantiles extension) validates its constructor arguments eagerly. The aggregator 'name' (the output column name) is required and cannot be null; the factory throws IllegalArgumentException immediately rather than failing later at query time. This guarantees every aggregator in a query spec has an addressable output name.

Source

Thrown at extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchAggregatorFactory.java:118

      final String name,
      final String fieldName,
      @Nullable final Integer k
  )
  {
    this(name, fieldName, k, null, DEFAULT_SHOULD_FINALIZE);
  }

  DoublesSketchAggregatorFactory(
      final String name,
      final String fieldName,
      @Nullable final Integer k,
      @Nullable final Long maxStreamLength,
      @Nullable final Boolean shouldFinalize,
      final byte cacheTypeId
  )
  {
    if (name == null) {
      throw new IAE("Must have a valid, non-null aggregator name");
    }
    this.name = name;
    if (fieldName == null) {
      throw new IAE("Parameter fieldName must be specified");
    }
    this.fieldName = fieldName;
    this.k = k == null ? DEFAULT_K : k;
    Util.checkIfIntPowerOf2(this.k, "k");
    this.maxStreamLength = maxStreamLength == null ? DEFAULT_MAX_STREAM_LENGTH : maxStreamLength;
    this.shouldFinalize = shouldFinalize == null ? DEFAULT_SHOULD_FINALIZE : shouldFinalize;
    this.cacheTypeId = cacheTypeId;
  }

  @Override
  public Aggregator factorize(final ColumnSelectorFactory metricFactory)
  {
    if (metricFactory.getColumnCapabilities(fieldName) != null
        && metricFactory.getColumnCapabilities(fieldName).isNumeric()) {

View on GitHub (pinned to 9b90983fd2)

Solutions

1. Add a non-null "name" field to the aggregation spec in the query JSON
2. In code, pass a valid output name string as the first constructor argument
3. If building from SQL, check that the planner-assigned aggregator name is not being overwritten with null

Example fix

// before
{"type":"quantilesDoublesSketch","fieldName":"value","k":128}
// after
{"type":"quantilesDoublesSketch","name":"sketch_agg","fieldName":"value","k":128}

if (aggregationSpec.get("name") == null || aggregationSpec.get("name").toString().isEmpty()) {
  throw new IllegalArgumentException("quantilesDoublesSketch aggregation requires a non-null 'name'");
}

boolean hasName(Map<String,Object> agg) { return agg.get("name") instanceof String && !((String) agg.get("name")).isEmpty(); }

When it happens

Trigger: Constructing a DoublesSketchAggregatorFactory with a null name via JSON (e.g. an aggregation entry missing the "name" field or set to null) or programmatically via the public constructor.

Common situations: Hand-written native JSON queries where the aggregation object omits "name"; SQL planner bugs or extension code building aggregators dynamically; deserializing a saved query spec that was truncated or hand-edited.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Parameter fieldName must be specified
• AggregatorFactoryNotMergeableException(this, other)
• ApproximateHistogramBufferAggregator does not support getFlo
• ApproximateHistogramBufferAggregator does not support getLon
• ApproximateHistogramBufferAggregator does not support getDou

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/3e54204a9b54b53c. Report an issue: GitHub.