apache/druid · error · IllegalArgumentException

Cannot accept both 'splitPoints' and 'numBins'

Error message

Cannot accept both 'splitPoints' and 'numBins'

What it means

The KllDoublesSketchToHistogramPostAggregator constructor validates that 'splitPoints' (explicit bin edges) and 'numBins' (auto-generated bin count) are mutually exclusive. Supplying both is ambiguous, so it throws IllegalArgumentException at construction time. Exactly one (or neither, defaulting bins) must be provided.

Source

Thrown at extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/kll/KllDoublesSketchToHistogramPostAggregator.java:62

  private final String name;
  private final PostAggregator field;
  private final double[] splitPoints;
  private final Integer numBins;

  @JsonCreator
  public KllDoublesSketchToHistogramPostAggregator(
      @JsonProperty("name") final String name,
      @JsonProperty("field") final PostAggregator field,
      @JsonProperty("splitPoints") @Nullable final double[] splitPoints,
      @JsonProperty("numBins") @Nullable final Integer numBins)
  {
    this.name = Preconditions.checkNotNull(name, "name is null");
    this.field = Preconditions.checkNotNull(field, "field is null");
    this.splitPoints = splitPoints;
    this.numBins = numBins;
    if (splitPoints != null && numBins != null) {
      throw new IAE("Cannot accept both 'splitPoints' and 'numBins'");
    }
  }

  @Override
  public Object compute(final Map<String, Object> combinedAggregators)
  {
    final KllDoublesSketch sketch = (KllDoublesSketch) field.compute(combinedAggregators);
    final int numBins = this.splitPoints != null ? this.splitPoints.length + 1 :
        (this.numBins != null ? this.numBins.intValue() : DEFAULT_NUM_BINS);
    if (numBins < 2) {
      throw new IAE("at least 2 bins expected");
    }
    if (sketch.isEmpty()) {
      final double[] histogram = new double[numBins];
      Arrays.fill(histogram, Double.NaN);
      return histogram;
    }
    final double[] splitPoints;

View on GitHub (pinned to 9b90983fd2)

Solutions

1. Remove either 'splitPoints' or 'numBins' from the post-aggregator spec, keeping only one
2. If you need explicit edges, delete numBins; if you want even bins, delete splitPoints
3. In spec-builder code, only emit the second field when the first is null

Example fix

// before
{"type":"kllDoublesSketchToHistogram","name":"h","field":f,"splitPoints":[1.0,2.0],"numBins":10}
// after
{"type":"kllDoublesSketchToHistogram","name":"h","field":f,"splitPoints":[1.0,2.0]}

Map<String,Object> spec = readSpec();
if (spec.containsKey("splitPoints") && spec.containsKey("numBins")) {
  throw new IllegalArgumentException("Provide only one of splitPoints and numBins");
}

try { new KllDoublesSketchToHistogramPostAggregator(name, field, sp, nb); } catch (IllegalArgumentException e) { log.error("Histogram spec invalid: {}", e.getMessage()); }

When it happens

Trigger: Constructing KllDoublesSketchToHistogramPostAggregator(name, field, splitPoints, numBins) with both arguments non-null — e.g. a JSON spec containing both "splitPoints": [...] and "numBins": 10.

Common situations: Copy-pasting a spec and adding numBins while forgetting to remove splitPoints; programmatic spec builders that set defaults for both fields; template-driven query generation.

Related errors

• at least 2 bins expected
• at least 2 bins expected
• Comparing histograms is not supported
• Comparing histograms is not supported
• Comparing arrays of quantiles is not supported

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/8bfc404df3390bb9. Report an issue: GitHub.