apache/druid · error · java.lang.IllegalArgumentException

A-Not-B requires at least 1 sketch

Error message

A-Not-B requires at least 1 sketch

What it means

sketchSetOperation() implements the NOT (A-Not-B) set operation, which mathematically needs at least one sketch (the A side). When the holders array is empty, there is nothing to compute, so it throws an IllegalArgumentException. Other operations (UNION/INTERSECT) tolerate empty inputs but NOT does not.

Source

Thrown at extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/SketchHolder.java:297

    //"true" returns an ordered sketch but slower to compute. advantage of ordered sketch
    //is that they are faster to "union" later but given that this method is used in
    //the final stages of query processing, ordered sketch would be of no use.
    switch (func) {
      case UNION:
        Union union = (Union) SetOperation.builder().setNominalEntries(sketchSize).build(Family.UNION);
        for (Object o : holders) {
          ((SketchHolder) o).updateUnion(union);
        }
        return SketchHolder.of(union);
      case INTERSECT:
        Intersection intersection = (Intersection) SetOperation.builder().setNominalEntries(sketchSize).build(Family.INTERSECTION);
        for (Object o : holders) {
          intersection.intersect(((SketchHolder) o).getSketch());
        }
        return SketchHolder.of(intersection.getResult(false, null));
      case NOT:
        if (holders.length < 1) {
          throw new IllegalArgumentException("A-Not-B requires at least 1 sketch");
        }

        if (holders.length == 1) {
          return (SketchHolder) holders[0];
        }

        Sketch result = ((SketchHolder) holders[0]).getSketch();
        for (int i = 1; i < holders.length; i++) {
          AnotB anotb = (AnotB) SetOperation.builder().setNominalEntries(sketchSize).build(Family.A_NOT_B);
          result = anotb.aNotB(result, ((SketchHolder) holders[i]).getSketch());
        }
        return SketchHolder.of(result);
      default:
        throw new IllegalArgumentException("Unknown sketch operation " + func);
    }
  }

  /**

View on GitHub (pinned to 9b90983fd2)

Solutions

1. Ensure at least one input sketch/field is provided for the NOT post-aggregator
2. Validate fields.size() >= 1 when constructing the SketchSetPostAggregator or building the query programmatically
3. If A may legitimately be absent, guard the call and return null or a default empty sketch instead of invoking NOT

Example fix

// before
Object[] holders = collectFields(); // may be empty
SketchHolder result = SketchHolder.sketchSetOperation(SketchHolder.Func.NOT, size, holders);
// after
if (holders.length < 1) {
  throw new IllegalArgumentException("NOT requires at least one input sketch field");
}
SketchHolder result = SketchHolder.sketchSetOperation(SketchHolder.Func.NOT, size, holders);

if (holders == null || holders.length < 1) {
  throw new IllegalArgumentException("NOT operation requires at least 1 input sketch");
}

boolean hasInputs(Object[] holders) {
  return holders != null && holders.length >= 1;
}

try {
  SketchHolder r = SketchHolder.sketchSetOperation(Func.NOT, size, holders);
} catch (IllegalArgumentException e) {
  // handle empty-input case: return null or empty sketch holder
}

When it happens

Trigger: Calling SketchHolder.sketchSetOperation(Func.NOT, size) with an empty Object[] holders array — e.g. a SketchSetPostAggregator whose field list resolved to zero sketches at runtime.

Common situations: A post-aggregator configured in a query whose input fields were filtered out or renamed, leaving zero dependencies; programmatic query building that passes an empty fields list for a NOT aggregator.

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

• Illegal number of fields[%s], must be > 1
• Comparing arrays of estimates and error bounds is not suppor
• Comparing histograms is not supported
• Cannot accept both 'splitPoints' and 'numBins'
• at least 2 bins expected

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/f789b84e86b8b0df. Report an issue: GitHub.