Index: lucene/CHANGES.txt
===================================================================
--- lucene/CHANGES.txt	(revision 935454)
+++ lucene/CHANGES.txt	(working copy)
@@ -219,6 +219,12 @@
   expressions).
   (Uwe Schindler, Robert Muir)
 
+* LUCENE-2402: IndexWriter.deleteUnusedFiles now deletes unreferenced commit
+  points too. If you use an IndexDeletionPolicy which holds onto index commits
+  (such as SnapshotDeletionPolicy), you can call this method to remove those
+  commit points when they are not needed anymore (instead of waiting for the 
+  next commit). (Shai Erera)
+  
 Bug fixes
 
 * LUCENE-2119: Don't throw NegativeArraySizeException if you pass
Index: lucene/src/java/org/apache/lucene/index/IndexWriter.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/IndexWriter.java	(revision 935454)
+++ lucene/src/java/org/apache/lucene/index/IndexWriter.java	(working copy)
@@ -4961,8 +4961,20 @@
    *  IndexWriter, you'll see the unused files linger.  If
    *  that's a problem, call this method to delete them
    *  (once you've closed the open readers that were
-   *  preventing their deletion). */
+   *  preventing their deletion). 
+   *  
+   *  <p> In addition, you can call this method to delete 
+   *  unreferenced index commits. This might be useful if you 
+   *  are using an {@link IndexDeletionPolicy} which holds
+   *  onto index commits until some criteria are met, but those
+   *  commits are no longer needed. Otherwise, those commits will
+   *  be deleted the next time commit() is called.
+   */
   public synchronized void deleteUnusedFiles() throws IOException {
-    deleter.deletePendingFiles();
+    synchronized (commitLock) {
+      deleter.checkpoint(rollbackSegmentInfos, true);
+//      deleter.checkpoint((SegmentInfos) segmentInfos.clone(), true);
+    }
   }
+  
 }
Index: lucene/src/test/org/apache/lucene/index/TestIndexWriter.java
===================================================================
--- lucene/src/test/org/apache/lucene/index/TestIndexWriter.java	(revision 935454)
+++ lucene/src/test/org/apache/lucene/index/TestIndexWriter.java	(working copy)
@@ -4915,6 +4915,40 @@
     }
   }
 
+  public void testDeleteUnsedFiles2() throws Exception {
+    // Validates that iw.deleteUnusedFiles() also deletes unused index commits
+    // in case a deletion policy which holds onto commits is used.
+    Directory dir = new MockRAMDirectory();
+    SnapshotDeletionPolicy sdp = new SnapshotDeletionPolicy(new KeepOnlyLastCommitDeletionPolicy());
+    IndexWriter writer = new IndexWriter(dir, new IndexWriterConfig(
+        TEST_VERSION_CURRENT, new WhitespaceAnalyzer(TEST_VERSION_CURRENT))
+        .setIndexDeletionPolicy(sdp));
+    
+    // First commit
+    Document doc = new Document();
+    doc.add(new Field("c", "val", Store.YES, Index.ANALYZED, TermVector.WITH_POSITIONS_OFFSETS));
+    writer.addDocument(doc);
+    writer.commit();
+    assertEquals(1, IndexReader.listCommits(dir).size());
+
+    // Keep that commit
+    sdp.snapshot();
+    
+    // Second commit - now KeepOnlyLastCommit cannot delete the prev commit.
+    doc = new Document();
+    doc.add(new Field("c", "val", Store.YES, Index.ANALYZED, TermVector.WITH_POSITIONS_OFFSETS));
+    writer.addDocument(doc);
+    writer.commit();
+    assertEquals(2, IndexReader.listCommits(dir).size());
+
+    // Should delete the unreferenced commit
+    sdp.release();
+    writer.deleteUnusedFiles();
+    assertEquals(1, IndexReader.listCommits(dir).size());
+    
+    writer.close();
+  }
+  
   private static class FlushCountingIndexWriter extends IndexWriter {
     int flushCount;
     public FlushCountingIndexWriter(Directory dir, IndexWriterConfig iwc) throws IOException {