What causes "${getClass().getName()} does not implement length" in apache/iceberg?

Call length() only on the DeleteWriteResult or the produced delete files after writer.close()/result(), not on the writer itself

apache/iceberg · error · UnsupportedOperationException

does not implement length

Error message

${getClass().getName()} does not implement length

What it means

SortingPositionOnlyDeleteWriter buffers position-only deletes in memory and sorts them before writing, so it cannot report a stable byte length mid-write; its length() override unconditionally throws UnsupportedOperationException. It is only intended to be queried after result() is obtained.

Solutions

Call length() only on the DeleteWriteResult or the produced delete files after writer.close()/result(), not on the writer itself
Check the writer type before querying length, or avoid SortingPositionOnlyDeleteWriter when byte length is needed incrementally
Get the equivalent size from the resulting DeleteFile(s) metadata after commit

Example fix

// before
long len = writer.length();
// after
writer.close();
long len = writer.result().deleteFiles().stream().mapToLong(DeleteFile::fileSizeInBytes).sum();

Defensive patterns

Strategy: validation

Validate before calling

if (writer instanceof SortingPositionOnlyDeleteWriter) { /* do not call length() before close */ }

Type guard

boolean supportsLength(DeleteWriter<?> w) { return !(w instanceof SortingPositionOnlyDeleteWriter); }

Try / catch

try { len = writer.length(); } catch (UnsupportedOperationException e) { len = -1; /* unknown until close */ }

Prevention

Query file sizes from DeleteWriteResult/DeleteFile after close, not from the writer
Document writer contracts where length is undefined mid-write
Avoid generic metrics code that assumes all writers implement length()

When it happens

Trigger: Calling length() on a SortingPositionOnlyDeleteWriter at any point (including during write), e.g. generic writer code that measures output size before closing the writer.

Common situations: Framework or metrics code that uniformly calls writer.length() to track file sizes; the sorting writer's size is unknown until deletes are written on close().

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/1c98395845c35f8a. Report an issue: GitHub.

Appendix: source

Thrown at core/src/main/java/org/apache/iceberg/deletes/SortingPositionOnlyDeleteWriter.java:92

      Function<CharSequence, PositionDeleteIndex> loadPreviousDeletes) {
    this.writers = writers;
    this.granularity = granularity;
    this.positionsByPath = CharSequenceMap.create();
    this.loadPreviousDeletes = loadPreviousDeletes;
  }

  @Override
  public void write(PositionDelete<T> positionDelete) {
    CharSequence path = positionDelete.path();
    long position = positionDelete.pos();
    PositionDeleteIndex positions =
        positionsByPath.computeIfAbsent(path, key -> new BitmapPositionDeleteIndex());
    positions.delete(position);
  }

  @Override
  public long length() {
    throw new UnsupportedOperationException(getClass().getName() + " does not implement length");
  }

  @Override
  public DeleteWriteResult result() {
    return result;
  }

  @Override
  public void close() throws IOException {
    if (result == null) {
      switch (granularity) {
        case FILE:
          this.result = writeFileDeletes();
          return;
        case PARTITION:
          this.result = writePartitionDeletes();
          return;
        default:

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