Github user davies commented on a diff in the pull request:

    https://github.com/apache/spark/pull/9969#discussion_r46179554
  
    --- Diff: 
core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorter.java
 ---
    @@ -521,4 +522,66 @@ public long getKeyPrefix() {
           return upstream.getKeyPrefix();
         }
       }
    +
    +  /**
    +   * Returns a iterator, which will return the rows in the order as 
inserted.
    +   *
    +   * It is the caller's responsibility to call `cleanupResources()`
    +   * after consuming this iterator.
    +   */
    +  public UnsafeSorterIterator getIterator() throws IOException {
    +    if (spillWriters.isEmpty()) {
    +      assert(inMemSorter != null);
    +      return inMemSorter.getIterator();
    +    } else {
    +      LinkedList<UnsafeSorterIterator> queue = new LinkedList<>();
    +      for (UnsafeSorterSpillWriter spillWriter : spillWriters) {
    +        queue.add(spillWriter.getReader(blockManager));
    +      }
    +      if (inMemSorter != null) {
    +        queue.add(inMemSorter.getIterator());
    +      }
    +      return new ChainedIterator(queue);
    +    }
    +  }
    +
    +  /**
    +   * Chain multiple UnsafeSorterIterator together as single one.
    +   */
    +  class ChainedIterator extends UnsafeSorterIterator {
    +
    +    private final Queue<UnsafeSorterIterator> iterators;
    +    private UnsafeSorterIterator current;
    +
    +    public ChainedIterator(Queue<UnsafeSorterIterator> iterators) {
    +      assert iterators.size() > 0;
    +      this.iterators = iterators;
    +      this.current = iterators.remove();
    +    }
    +
    +    @Override
    +    public boolean hasNext() {
    +      if (!current.hasNext() && !iterators.isEmpty()) {
    +        current = iterators.remove();
    --- End diff --
    
    Oh, I see, thanks, will fix it.


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