apache/druid · error · IllegalArgumentException

Object cannot be deserialized to a DDSketch Sketch: " +…

Error message

Object cannot be deserialized to a DDSketch Sketch: " + serializedSketch.getClass()

What it means

DDSketchUtils.deserialize accepts a base64 String or a raw byte[] protobuf sketch; any other object type (e.g. a Map decoded from JSON) reaches the final throw because it cannot be decoded into a DDSketch.

Solutions

1. Ensure the value was produced by DDSketchUtils.serialize (base64 String or byte[]).
2. Fix the query/ingestion wiring that passes the wrong object type.

When it happens

Trigger: Thrown at extensions-contrib/ddsketch/src/main/java/org/apache/druid/query/aggregation/ddsketch/DDSketchUtils.java:55 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/48dd76389205735f. Report an issue: GitHub.

Appendix: source

Thrown at extensions-contrib/ddsketch/src/main/java/org/apache/druid/query/aggregation/ddsketch/DDSketchUtils.java:55

  }

  public static DDSketch deserialize(Object serializedSketch)
  {
    try {
      if (serializedSketch instanceof String) {
        String str = (String) serializedSketch;
        byte[] bytes = StringUtils.decodeBase64(StringUtils.toUtf8(str));
        com.datadoghq.sketch.ddsketch.proto.DDSketch proto = com.datadoghq.sketch.ddsketch.proto.DDSketch.parseFrom(bytes);
        DDSketch recovered = DDSketchProtoBinding.fromProto(() -> new CollapsingLowestDenseStore(1000), proto);
        return recovered;
      } else if (serializedSketch instanceof byte[]) {
        com.datadoghq.sketch.ddsketch.proto.DDSketch proto = com.datadoghq.sketch.ddsketch.proto.DDSketch.parseFrom((byte[]) serializedSketch);
        DDSketch recovered = DDSketchProtoBinding.fromProto(() -> new CollapsingLowestDenseStore(1000), proto);
        return recovered;
      } 
    }
    catch (InvalidProtocolBufferException e) {
      throw new IAE(
          "Object cannot be deserialized to a DDSketch Sketch: "
          + serializedSketch.getClass()
      );
    }
    if (serializedSketch instanceof DDSketch) {
      return (DDSketch) serializedSketch;
    }
    throw new IAE(
        "Object cannot be deserialized to a DDSketch Sketch: "
        + serializedSketch.getClass()
    );
  }

  static byte[] toBytes(DDSketch sketch)
  {
    return DDSketchProtoBinding.toProto(sketch).toByteArray();
  }

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