What causes "Remove is not supported" in apache/iceberg?

Do not call remove(); iterate read-only and collect the rows you need.

apache/iceberg · error · UnsupportedOperationException

Remove is not supported

Error message

Remove is not supported

What it means

DVIterator implements Java's legacy Iterator interface, whose remove() default operation is unsupported. Iceberg's iterator over rows feeding deletion-vector writes is read-only, so any call to remove() fails fast rather than corrupting state. This is a deliberate guard: removal is meaningless for a scan-backed stream.

Source

Thrown at spark/v3.5/spark/src/main/java/org/apache/iceberg/spark/source/DVIterator.java:104

          rowValues.add(ScanTaskUtil.contentSizeInBytes(deleteFile));
        } else if (fieldId == MetadataColumns.DELETE_FILE_ROW_FIELD_ID) {
          // DVs don't track the row that was deleted
          rowValues.add(null);
        }
      }

      this.row = new GenericInternalRow(rowValues.toArray());
    } else if (null != deletedPositionIndex) {
      // only update the deleted position if necessary, everything else stays the same
      row.update(deletedPositionIndex, position);
    }

    return row;
  }

  @Override
  public void remove() {
    throw new UnsupportedOperationException("Remove is not supported");
  }

  @Override
  public void close() {}
}

View on GitHub (pinned to 86d9c8fc54)

Solutions

Do not call remove(); iterate read-only and collect the rows you need.
If filtering is required, filter upstream in the scan/plan instead of mutating during iteration.
Use CloseableIterable.filter for filtered views instead of Iterator.remove.

Example fix

// before
while (it.hasNext()) {
  Row r = it.next();
  if (!keep(r)) { it.remove(); } // throws
}
// after
CloseableIterable<Row> kept = CloseableIterable.filter(rows, this::keep);

Defensive patterns

Strategy: type-guard

Type guard

if (iterator instanceof DVIterator) { /* never call remove(); treat as read-only */ }

Prevention

Treat all Iceberg scan iterators as read-only
Never use Iterator.remove() on data returned from Iceberg scans
Prefer CloseableIterable.filter/combiner over mutation during iteration

When it happens

Trigger: Calling remove() on the Iterator returned by DVIterator, e.g. code that iterates rows and mutates the underlying collection via iterator.remove().

Common situations: Legacy Java code or third-party utilities that use Iterator.remove() while draining scan results passed into deletion-vector-producing readers.

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/c1dc36b244d7babe. Report an issue: GitHub.