apache/iceberg · error · UnsupportedOperationException

Variant column only supports getVariant()

Error message

Variant column only supports getVariant()

What it means

VariantColumnVector models a Spark VARIANT column as two child vectors (value at ordinal 0, metadata at ordinal 1). getBoolean() has no meaningful mapping to that pair, so it throws UnsupportedOperationException — only getVariant()/getChild are supported for variant columns.

Solutions

1. Read the value with getVariant(rowId) instead
2. Cast the variant explicitly via variant functions in Spark rather than in the column vector
3. Add a VariantType guard in code that iterates batch columns

Example fix

// before
boolean b = columnVector.getBoolean(rowId);
// after
Object variant = columnVector.getVariant(rowId);

if (!(dataType instanceof org.apache.spark.sql.types.VariantType)) { return columnVector.getBoolean(rowId); }

boolean canGetBoolean(ColumnVector cv, org.apache.spark.sql.types.DataType t) { return !(t instanceof org.apache.spark.sql.types.VariantType); }

try { b = cv.getBoolean(rowId); } catch (UnsupportedOperationException e) { if (e.getMessage() != null && e.getMessage().contains("only supports getVariant")) { b = extractBoolean(cv.getVariant(rowId)); } else { throw e; } }

When it happens

Trigger: Calling getBoolean(rowId) on a variant-typed column in a ColumnarBatch produced by Iceberg's vectorized reader; commonly from generic per-row extraction code or an engine that resolved a variant-to-boolean cast to the raw column vector.

Common situations: Custom code reading all columns of a batch by primitive accessors; queries forcing variant-to-boolean casts; compatibility shims porting Iceberg batches into engines that expect plain typed vectors.

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

• Variant column only supports getVariant()
• Variant column only supports getVariant()
• Cannot add column since setting default values in Spark is…
• Cannot convert unknown expression
• Deleted rows scan task is not supported yet

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/e08b07c9aa005a22. Report an issue: GitHub.

Appendix: source

Thrown at spark/v4.1/spark/src/main/java/org/apache/iceberg/spark/data/vectorized/VariantColumnVector.java:80

    return valueChild.isNullAt(rowId);
  }

  // getChild is what getVariant() calls: child(0) = value, child(1) = metadata
  @Override
  public ColumnVector getChild(int ordinal) {
    if (ordinal == 0) {
      return valueChild;
    } else if (ordinal == 1) {
      return metadataChild;
    }

    throw new IllegalArgumentException(
        "Variant column has only 2 children, got ordinal: " + ordinal);
  }

  @Override
  public boolean getBoolean(int rowId) {
    throw unsupported();
  }

  @Override
  public byte getByte(int rowId) {
    throw unsupported();
  }

  @Override
  public short getShort(int rowId) {
    throw unsupported();
  }

  @Override
  public int getInt(int rowId) {
    throw unsupported();
  }

  @Override

View on GitHub (pinned to 86d9c8fc54)