apache/druid · error · UnsupportedColumnTypeException

Cannot handle column

Error message

Cannot handle column [%s] with type [%s]

What it means

FrameColumnWriters.create's switch over ColumnType falls through to default when the type family (or array element type within a family) has no corresponding writer. It throws UnsupportedColumnTypeException(column, type) naming the concrete unsupported type. This covers exotic complex types or array element types the frame writer cannot encode.

Solutions

1. Cast the column to a supported type in the SQL/spec before frame writing
2. Upgrade Druid so both sides support the type, or exclude the column from the output
3. Check FrameColumnWriters.create's supported types before selecting columns for frame output
4. File/patch support for the missing ColumnType case if legitimate

Example fix

// before
SELECT someNewTypeCol FROM ...
// after
SELECT CAST(someNewTypeCol AS VARCHAR) AS someNewTypeCol FROM ...

ColumnType t = signature.getColumnType(idx).orElse(null); if (t != null && !SUPPORTED_WRITE_TYPES.contains(t.getFamily())) { /* cast or drop */ }

boolean isWritableType(ColumnType t) { return t != null && (t.is(LONG)||t.is(FLOAT)||t.is(DOUBLE)||t.is(STRING)||t.isArray()||t.is(COMPLEX)); }

try { writer = FrameColumnWriters.create(...); } catch (UnsupportedColumnTypeException e) { log.warn("Unwritable column {} type {}", e.getColumnName(), e.getColumnType()); }

When it happens

Trigger: Writing a frame column whose ColumnType is a family other than LONG/FLOAT/DOUBLE/STRING/ARRAY/COMPLEX branches (or an array with unsupported element type), e.g. a newly added type not yet mapped in the switch.

Common situations: Version skew where a writer node emits a type older readers/writers don't know; querying with expression results of new types; ingestion specs introducing complex types not supported by the frame format.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Cannot handle column
• Cannot handle column
• Cannot create comparator for array type
• Cannot handle column
• Cannot handle column

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/550b2180d049307f. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/frame/write/columnar/FrameColumnWriters.java:90

        return makeLongWriter(columnSelectorFactory, allocator, column);
      case FLOAT:
        return makeFloatWriter(columnSelectorFactory, allocator, column);
      case DOUBLE:
        return makeDoubleWriter(columnSelectorFactory, allocator, column);
      case STRING:
        return makeStringWriter(columnSelectorFactory, allocator, column);
      case ARRAY:
        switch (type.getElementType().getType()) {
          case STRING:
            return makeStringArrayWriter(columnSelectorFactory, allocator, column);
          case LONG:
            return makeLongArrayWriter(columnSelectorFactory, allocator, column);
          case FLOAT:
            return makeFloatArrayWriter(columnSelectorFactory, allocator, column);
          case DOUBLE:
            return makeDoubleArrayWriter(columnSelectorFactory, allocator, column);
          default:
            throw new UnsupportedColumnTypeException(column, type);
        }
      case COMPLEX:
        return makeComplexWriter(columnSelectorFactory, allocator, column, type.getComplexTypeName());
      default:
        throw new UnsupportedColumnTypeException(column, type);
    }
  }

  private static LongFrameColumnWriter makeLongWriter(
      final ColumnSelectorFactory selectorFactory,
      final MemoryAllocator allocator,
      final String columnName
  )
  {
    final ColumnCapabilities capabilities = selectorFactory.getColumnCapabilities(columnName);
    final ColumnValueSelector<?> selector =
        TypeCastSelectors.makeColumnValueSelector(selectorFactory, columnName, ColumnType.LONG);
    return new LongFrameColumnWriter(selector, allocator, hasNullsForNumericWriter(capabilities));

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