apache/druid · error · SegmentValidationException

Dim [ ] values not equal. Expected found

Error message

Dim [%s] values not equal. Expected %s found %s

What it means

IndexIO.validateTwoSegments compares corresponding rows/columns of two segments and throws a ValidationException 'Dim [%s] values not equal. Expected %s found %s' when a dimension's null-ness differs between the two segments for the same row. Here exactly one of the two values is a null row (isNullRow XOR). This guard detects segment corruption or divergence between replicas/converted segments.

Solutions

1. Re-ingest or re-generate the segment from source data.
2. Compare against the correct counterpart segment; verify you validated the intended pair.
3. Check for segment corruption with the segment's metadata/hash and restore from deep storage.

Example fix

// before
indexIO.validateTwoSegments(expectedSegment, convertedSegment);
// after
// regenerate the mismatching segment instead of validating
Segment fixed = segmentCreator.buildFromSource(sourceData);
indexIO.validateTwoSegments(expectedSegment, fixed);

// pre-check null-ness parity before validation
boolean nullParity = isNullRow(vals1) == isNullRow(vals2);
if (!nullParity) { regenerateSegment(); }

try { indexIO.validateTwoSegments(a, b); } catch (ValidationException e) { log.error("Segment mismatch: {}", e.getMessage()); regenerateFromSource(); }

When it happens

Trigger: Running validateTwoSegments (e.g. segment conversion validation, replacement validation) where at row i for dimension i, one segment holds a null row and the other holds a non-null value.

Common situations: Verifying segments after Druid version upgrades or index conversion; comparing replaced/historical segments; corrupted partial data written by a buggy ingestion run.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• A-Not-B requires at least 1 sketch
• Access-Check-Result
• Action [ ] failed for worker [ ] with status ( )
• Actual Row count mismatch. Expected
• Aggregation [ ] does not support column [ ] of type [ ]…

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/da401e5024dcf2bb. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/segment/IndexIO.java:283

      final String dim2Name = dim2Names.get(i);

      ColumnCapabilities capabilities1 = adapter1.getCapabilities(dim1Name);
      ColumnCapabilities capabilities2 = adapter2.getCapabilities(dim2Name);
      ColumnType dim1Type = capabilities1.toColumnType();
      ColumnType dim2Type = capabilities2.toColumnType();
      if (!Objects.equals(dim1Type, dim2Type)) {
        throw new SegmentValidationException(
            "Dim [%s] types not equal. Expected %d found %d",
            dim1Name,
            dim1Type,
            dim2Type
        );
      }

      Object vals1 = dims1.get(i);
      Object vals2 = dims2.get(i);
      if (isNullRow(vals1) ^ isNullRow(vals2)) {
        throw notEqualValidationException(dim1Name, vals1, vals2);
      }
      boolean vals1IsList = vals1 instanceof List;
      boolean vals2IsList = vals2 instanceof List;
      if (vals1IsList ^ vals2IsList) {
        if (vals1IsList) {
          if (((List) vals1).size() != 1 || !Objects.equals(((List) vals1).get(0), vals2)) {
            throw notEqualValidationException(dim1Name, vals1, vals2);
          }
        } else {
          if (((List) vals2).size() != 1 || !Objects.equals(((List) vals2).get(0), vals1)) {
            throw notEqualValidationException(dim1Name, vals1, vals2);
          }
        }
      } else if (vals1 instanceof Object[]) {
        if (!Arrays.deepEquals((Object[]) vals1, (Object[]) vals2)) {
          throw notEqualValidationException(dim1Name, vals1, vals2);
        }
      } else {

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