apache/druid · warning

Compression value [ ] is greater than the max allowed…

Error message

Compression value [%d] is greater than the max allowed compression value [%d]. Setting it to max allowed value

What it means

TDigestSketchAggregatorFactory warns and clamps when the requested t-digest compression exceeds the maximum allowed by TDigestSketchConfig.maxCompression. The constructor does not throw; it silently sets compression to the max allowed value. This protects memory usage since compression drives sketch size.

Solutions

1. Lower the compression parameter in the aggregator spec to be <= maxCompression
2. Or raise druid.query.tDigest.maxCompression in the runtime config if the larger sketch is intentional and memory allows
3. Check the warning in logs to confirm which value was clamped; recompute expected memory footprint
4. Align compression values between ingestion and query specs to keep results consistent

Example fix

// before
{"type":"TDigestSketch","fieldName":"latency","compression":1000} // max is 500
// after
{"type":"TDigestSketch","fieldName":"latency","compression":500}

Integer max = tdigestConfig.getMaxCompression();
if (compression != null && max != null && compression > max) {
    compression = max; // clamp before constructing the factory
}

When it happens

Trigger: Creating a TDigestSketch aggregator/post-aggregator with a compression parameter larger than the value configured in druid.query.tDigest.maxCompression (or in the TDigestSketchModule config).

Common situations: A query or ingestion spec written for an environment with no maxCompression cap is reused where a cap was added; operator lowers maxCompression globally; typos producing huge compression values like 10000.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

• maxStringBytes must be greater than 0
• Aggregation [ ] does not support column [ ] of type [ ]…
• Aggregator[ ] cannot vectorize
• AggregatorFactoryNotMergeableException
• AggregatorFactoryNotMergeableException

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/9b8d5f4b212dce77. Report an issue: GitHub.

Appendix: source

Thrown at extensions-contrib/tdigestsketch/src/main/java/org/apache/druid/query/aggregation/tdigestsketch/TDigestSketchAggregatorFactory.java:109

      @JacksonInject final TDigestConfig tDigestConfig
  )
  {
    this(name, fieldName, compression, AggregatorUtil.TDIGEST_BUILD_SKETCH_CACHE_TYPE_ID, tDigestConfig);
  }

  TDigestSketchAggregatorFactory(
      final String name,
      final String fieldName,
      @Nullable final Integer compression,
      final byte cacheTypeId,
      final TDigestConfig tDigestConfig
  )
  {
    this.name = Objects.requireNonNull(name, "Must have a valid, non-null aggregator name");
    this.fieldName = Objects.requireNonNull(fieldName, "Parameter fieldName must be specified");
    this.tDigestConfig = tDigestConfig;
    if (tDigestConfig.getMaxCompression() != null && compression != null && compression > tDigestConfig.getMaxCompression()) {
      log.warn(
          "Compression value [%d] is greater than the max allowed compression value [%d]. Setting it to max allowed value",
          compression,
          tDigestConfig.getMaxCompression()
      );
      this.compression = tDigestConfig.getMaxCompression();
    } else {
      this.compression = Configs.valueOrDefault(compression, DEFAULT_COMPRESSION);
    }
    this.cacheTypeId = cacheTypeId;
  }


  @Override
  public byte[] getCacheKey()
  {
    return new CacheKeyBuilder(
        cacheTypeId
    ).appendString(fieldName).appendInt(compression).build();

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