apache/iceberg · error · java.lang.UnsupportedOperationException

Cannot set row kind in the RowDataProjection

Error message

Cannot set row kind in the RowDataProjection

What it means

RowDataProjection wraps an inner RowData and projects it to a subset of fields. Setting the row kind on a projection is not a meaningful operation, so setRowKind unconditionally throws UnsupportedOperationException. This is an intentionally unsupported mutating method on a read-only projection view.

Solutions

  1. Wrap the projected row in a copy (e.g. GenericRowData) and set the kind on that copy
  2. Use a BinaryRowData/JoinedRowData wrapper that supports row kind
  3. Apply the row-kind change upstream, before or after projection, on your own RowData

Example fix

// before
projected.setRowKind(RowKind.DELETE); // throws
// after
GenericRowData copy = new GenericRowData(projected.getArity());
for (int i = 0; i < projected.getArity(); i++) copy.setField(i, RowData.createFieldGetter(...).getFieldOrNull(projected));
copy.setRowKind(RowKind.DELETE);
Defensive patterns

Strategy: fallback

Type guard

RowData mutable = (projected instanceof RowDataProjection) ? copyOf(projected) : projected;

Try / catch

try { row.setRowKind(kind); } catch (UnsupportedOperationException e) { GenericRowData copy = copyToGenericRowData(row); copy.setRowKind(kind); emit(copy); }

Prevention

When it happens

Trigger: Calling setRowKind(...) on a RowDataProjection instance obtained from Iceberg's Flink source/scan pipeline (e.g. attempting to mark a projected row as INSERT/DELETE before emitting to a sink).

Common situations: Custom Flink operators or sinks that assume any RowData is mutable and call setRowKind; UDFs that re-tag rows downstream of the Iceberg reader.

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

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/b5c95f48f868517f. Report an issue: GitHub.

Appendix: source

Thrown at flink/v2.1/flink/src/main/java/org/apache/iceberg/flink/data/RowDataProjection.java:198

  private Object getValue(int pos) {
    Preconditions.checkState(rowData != null, "Row data not wrapped");
    return getters[pos].getFieldOrNull(rowData);
  }

  @Override
  public int getArity() {
    return getters.length;
  }

  @Override
  public RowKind getRowKind() {
    Preconditions.checkState(rowData != null, "Row data not wrapped");
    return rowData.getRowKind();
  }

  @Override
  public void setRowKind(RowKind kind) {
    throw new UnsupportedOperationException("Cannot set row kind in the RowDataProjection");
  }

  @Override
  public boolean isNullAt(int pos) {
    return getValue(pos) == null;
  }

  @Override
  public boolean getBoolean(int pos) {
    return (boolean) getValue(pos);
  }

  @Override
  public byte getByte(int pos) {
    return (byte) getValue(pos);
  }

  @Override

View on GitHub (pinned to 86d9c8fc54)