apache/druid · error · IllegalArgumentException

Parameter fieldName must be specified

Error message

Parameter fieldName must be specified

What it means

DoublesSketchAggregatorFactory requires a non-null fieldName identifying the input column that holds the doubles to sketch. If fieldName is null the factory throws IllegalArgumentException at construction, because the aggregator would have nothing to aggregate over.

Source

Thrown at extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchAggregatorFactory.java:122

  {
    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()) {
      final ColumnValueSelector<Double> selector = metricFactory.makeColumnValueSelector(fieldName);
      if (selector instanceof NilColumnValueSelector) {
        return new NoopDoublesSketchAggregator();
      }

View on GitHub (pinned to 9b90983fd2)

Solutions

1. Add a valid "fieldName" pointing to an existing numeric input column in the query JSON
2. Verify the input column exists in the segment schema and is a numeric type
3. In Java code, pass the input column name as the second constructor argument

Example fix

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

if (aggregationSpec.get("fieldName") == null) {
  throw new IllegalArgumentException("quantilesDoublesSketch aggregation requires a 'fieldName' input column");
}

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

When it happens

Trigger: Constructing DoublesSketchAggregatorFactory with fieldName == null, e.g. a JSON aggregation spec missing "fieldName" or referencing a null field after programmatic assembly.

Common situations: Hand-written native queries missing "fieldName"; ingesting/rolling-up specs where the input column was renamed; copying an aggregator spec and accidentally dropping the field key.

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

• Must have a valid, non-null aggregator name
• 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/b646f134ac902ab2. Report an issue: GitHub.