apache/druid · error · RE

Unknown version

Error message

Unknown version

What it means

NestedDataColumnSupplierV4.read() recognizes only version byte V4. Any other version byte throws RE 'Unknown version <n>'. Since this supplier only handles V4, encountering another version means the column was written by a different (usually newer) format version or the file is damaged.

Source

Thrown at processing/src/main/java/org/apache/druid/segment/nested/NestedDataColumnSupplierV4.java:215

            fields,
            fieldInfo,
            compressedRawColumnSupplier,
            nullValues,
            stringDictionarySupplier,
            longDictionarySupplier,
            doubleDictionarySupplier,
            arrayDictionarySupplier,
            mapper,
            NestedCommonFormatColumnFormatSpec.builder().setBitmapEncoding(metadata.getBitmapSerdeFactory()).build(),
            metadata.getByteOrder(),
            simpleType
        );
      }
      catch (IOException ex) {
        throw new RE(ex, "Failed to deserialize V%s column.", version);
      }
    } else {
      throw new RE("Unknown version " + version);
    }
  }

  private final byte version;
  private final String columnName;
  private final ColumnConfig columnConfig;
  private final Supplier<? extends Indexed<ByteBuffer>> fieldsSupplier;
  private final FieldTypeInfo fieldInfo;
  private final CompressedVariableSizedBlobColumnSupplier compressedRawColumnSupplier;
  private final ImmutableBitmap nullValues;
  private final Supplier<? extends Indexed<ByteBuffer>> stringDictionarySupplier;
  private final Supplier<FixedIndexed<Long>> longDictionarySupplier;
  private final Supplier<FixedIndexed<Double>> doubleDictionarySupplier;
  private final Supplier<FrontCodedIntArrayIndexed> arrayDictionarySupplier;
  private final SegmentFileMapper fileMapper;

  @Nullable
  private final ColumnType simpleType;

View on GitHub (pinned to 9b90983fd2)

Solutions

  1. Use/upgrade to the Druid version matching the column's serialized version.
  2. Let the correct supplier for the version handle the column (check NestedDataColumnSupplier dispatch logic).
  3. Re-ingest to rewrite columns in the supported format.
  4. Restore the segment from deep storage if the header is corrupted.
Defensive patterns

Strategy: type-guard

Validate before calling

byte version = data.get(0);
if (version != 4) { /* dispatch to the correct supplier for this version */ }

Type guard

boolean isV4(byte v) { return v == 4; }

Try / catch

try {
  col = v4Supplier.get();
} catch (RE e) {
  if (e.getMessage().startsWith("Unknown version")) {
    log.warn("Non-V4 column handed to V4 supplier; re-dispatch");
  } throw e;
}

Prevention

When it happens

Trigger: Opening a column whose version byte differs from V4 (e.g. written as V1-V3 handled by another supplier, or a V5+ from a newer Druid, or garbage bytes).

Common situations: Wiring the V4 supplier against non-V4 columns; newer writer version read by older cluster; corrupt column headers.

Understand the failure class

Background: "is not a compatible type" / "cannot merge" errors: when a value's type doesn't match what the library requires — this error's family across 65 libraries.

Related errors

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/c015d22e28e17388. Report an issue: GitHub.