apache/iceberg · error · UnsupportedOperationException

Unsupported table change: DropWatermark.

Error message

Unsupported table change: DropWatermark.

What it means

Guard in FlinkAlterTableUtil.applySchemaChanges: a DropWatermark table change was received. Since Iceberg schemas have no watermark concept, there is nothing to drop and the change is rejected rather than silently ignored.

Source

Thrown at flink/v1.20/flink/src/main/java/org/apache/iceberg/flink/util/FlinkAlterTableUtil.java:139

   * @param schemaChanges a list of Flink table changes
   */
  public static void applySchemaChanges(
      UpdateSchema pendingUpdate, List<TableChange> schemaChanges) {
    for (TableChange change : schemaChanges) {
      if (change instanceof TableChange.AddColumn) {
        applyAddColumn(pendingUpdate, (TableChange.AddColumn) change);
      } else if (change instanceof TableChange.ModifyColumn) {
        TableChange.ModifyColumn modifyColumn = (TableChange.ModifyColumn) change;
        applyModifyColumn(pendingUpdate, modifyColumn);
      } else if (change instanceof TableChange.DropColumn) {
        TableChange.DropColumn dropColumn = (TableChange.DropColumn) change;
        pendingUpdate.deleteColumn(dropColumn.getColumnName());
      } else if (change instanceof TableChange.AddWatermark) {
        throw new UnsupportedOperationException("Unsupported table change: AddWatermark.");
      } else if (change instanceof TableChange.ModifyWatermark) {
        throw new UnsupportedOperationException("Unsupported table change: ModifyWatermark.");
      } else if (change instanceof TableChange.DropWatermark) {
        throw new UnsupportedOperationException("Unsupported table change: DropWatermark.");
      } else if (change instanceof TableChange.AddUniqueConstraint) {
        TableChange.AddUniqueConstraint addPk = (TableChange.AddUniqueConstraint) change;
        applyUniqueConstraint(pendingUpdate, addPk.getConstraint());
      } else if (change instanceof TableChange.ModifyUniqueConstraint) {
        TableChange.ModifyUniqueConstraint modifyPk = (TableChange.ModifyUniqueConstraint) change;
        applyUniqueConstraint(pendingUpdate, modifyPk.getNewConstraint());
      } else if (change instanceof TableChange.DropConstraint) {
        throw new UnsupportedOperationException("Unsupported table change: DropConstraint.");
      } else {
        throw new UnsupportedOperationException("Cannot apply unknown table change: " + change);
      }
    }
  }

  private static void applyAddColumn(UpdateSchema pendingUpdate, TableChange.AddColumn addColumn) {
    Column flinkColumn = addColumn.getColumn();
    Preconditions.checkArgument(
        FlinkCompatibilityUtil.isPhysicalColumn(flinkColumn),

View on GitHub (pinned to 86d9c8fc54)

Solutions

1. Remove the DROP WATERMARK clause from the statement
2. Skip watermark changes entirely when migrating to Iceberg (they are implicitly absent)
3. Filter the TableChange list before calling applySchemaChanges

if (changes.stream().anyMatch(c -> c instanceof TableChange.DropWatermark)) {
  throw new IllegalArgumentException("Watermark changes are unsupported on Iceberg tables");
}

try {
  FlinkAlterTableUtil.applySchemaChanges(table, changes);
} catch (UnsupportedOperationException e) {
  // ignore or log: watermark is implicitly absent in Iceberg
}

When it happens

Trigger: Executing `ALTER TABLE ... DROP WATERMARK` against an Iceberg-backed Flink table.

Common situations: Cleaning up Flink-specific DDL when switching a table from a Flink-native catalog to Iceberg; schema-sync tooling replaying full table definitions.

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

• Unsupported table change: AddWatermark.
• Unsupported table change: ModifyWatermark.
• Creating table with watermark specs is not supported yet.
• Unsupported table change: AddWatermark.
• Unsupported table change: ModifyWatermark.

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/a9a683efe4b68de1. Report an issue: GitHub.