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

Do not call remove(); collect the records you want to keep into a new collection instead.

apache/iceberg · error · UnsupportedOperationException

Remove is not supported

Error message

Remove is not supported

What it means

ParquetIterator.remove() is unsupported: Parquet files are immutable, so iterator element removal is a protocol violation. It always throws UnsupportedOperationException with the message "Remove is not supported".

Solutions

Do not call remove(); collect the records you want to keep into a new collection instead.
If deletion is intended, delete data files via Iceberg delete operations (DeleteFiles), not the iterator.
Wrap the iterator with Guava's Iterators.unmodifiableIterator to surface misuse early.

Example fix

// before
if (!predicate.test(row)) { it.remove(); }
// after
if (predicate.test(row)) { kept.add(row); }

Defensive patterns

Strategy: type-guard

Try / catch

try {
  it.remove();
} catch (UnsupportedOperationException e) {
  LOG.warn("Cannot remove from parquet iterator; collect keepers instead");
}

Prevention

Treat Parquet-backed iterators as read-only.
Filter by collecting wanted records, not removing unwanted ones.
Use Iceberg delete APIs for actual data removal.

When it happens

Trigger: Calling remove() on an iterator obtained from ParquetIterable.iterator(), directly or indirectly (e.g. via a collection/helper that mutates while iterating).

Common situations: Framework code that assumes mutable iterators (e.g. filtering by removing elements); porting code from in-memory collections to Parquet-backed iteration.

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/f678eb743d2d80d0. Report an issue: GitHub.

Appendix: source

Thrown at parquet/src/main/java/org/apache/iceberg/parquet/ParquetIterable.java:91

      return next;
    }

    private T advance() {
      // this must be called in hasNext because it reuses an UnsafeRow
      try {
        T nextRecord = parquet.read();
        this.needsAdvance = false;
        this.hasNext = nextRecord != null;
        return nextRecord;
      } catch (IOException e) {
        throw new RuntimeIOException(e);
      }
    }

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

    @Override
    public void close() throws IOException {
      parquet.close();
    }
  }
}

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