apache/druid · error · IllegalArgumentException

Expected a string with a number, received value

Error message

Expected a string with a number, received value 

What it means

TDigestSketchComplexMetricSerde.extractValue accepts raw values that are null, Number, or MergingDigest, and strings only if they look like a number (start with a digit) or decode as a base64-encoded MergingDigest (which always starts with 'A'). The error fires when a string value matches neither shape, meaning the row column contains arbitrary text that cannot be interpreted as sketch input.

Solutions

1. Ensure the input column contains numeric values or base64-encoded MergingDigest strings
2. Fix the ingestion spec (parseSpec/flattener) so the field is parsed as a number or sketch, not raw text
3. Preprocess or filter out rows whose sketch column holds non-numeric, non-base64 strings

When it happens

Trigger: Thrown at extensions-contrib/tdigestsketch/src/main/java/org/apache/druid/query/aggregation/tdigestsketch/TDigestSketchComplexMetricSerde.java:67 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/893ef632cb9f020b. Report an issue: GitHub.

Appendix: source

Thrown at extensions-contrib/tdigestsketch/src/main/java/org/apache/druid/query/aggregation/tdigestsketch/TDigestSketchComplexMetricSerde.java:67

      @Override
      public Object extractValue(final InputRow inputRow, final String metricName)
      {
        final Object object = inputRow.getRaw(metricName);
        if (object == null || object instanceof Number || object instanceof MergingDigest) {
          return object;
        }
        if (object instanceof String) {
          String objectString = (String) object;
          if (Character.isDigit((objectString).charAt(0))) {
            // Base64 representation of MergingDigest starts with A. So if it's a
            // string that starts with a digit, we assume it is a number.
            try {
              Double doubleValue = Double.parseDouble(objectString);
              return doubleValue;
            }
            catch (NumberFormatException e) {
              throw new IAE("Expected a string with a number, received value " + objectString);
            }
          }
        }
        return TDigestSketchUtils.deserialize(object);
      }
    };
  }

  @Override
  public ObjectStrategy<MergingDigest> getObjectStrategy()
  {
    return STRATEGY;
  }
}

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