HDFS-4700. Fix the undo section of rename with snapshots. Contributed by Jing Zhao

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-2802@1468632 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/CHANGES.HDFS-2802.txt

@@ -241,3 +241,6 @@ Branch-2802 Snapshot (Unreleased)
   create a file/directory with ".snapshot" as the name.  If ".snapshot" is used
   in a previous version of HDFS, it must be renamed before upgrade; otherwise,
   upgrade will fail.  (szetszwo)
+
+  HDFS-4700. Fix the undo section of rename with snapshots.  (Jing Zhao via
+  szetszwo)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirectory.java

@@ -62,6 +62,7 @@ import org.apache.hadoop.hdfs.server.blockmanagement.DatanodeDescriptor;
 import org.apache.hadoop.hdfs.server.common.HdfsServerConstants.BlockUCState;
 import org.apache.hadoop.hdfs.server.namenode.INode.BlocksMapUpdateInfo;
 import org.apache.hadoop.hdfs.server.namenode.INodeDirectory.INodesInPath;
+import org.apache.hadoop.hdfs.server.namenode.INodeReference.WithCount;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.INodeDirectorySnapshottable;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.INodeDirectoryWithSnapshot;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.Snapshot;
@@ -582,12 +583,17 @@ public class FSDirectory implements Closeable {
     
     // check srcChild for reference
     final INodeReference.WithCount withCount;
-    if (srcChildIsReference || isSrcInSnapshot) {
+    int srcRefDstSnapshot = srcChildIsReference ? srcChild.asReference()
+        .getDstSnapshotId() : Snapshot.INVALID_ID;
+    if (isSrcInSnapshot) {
       final INodeReference.WithName withName = srcIIP.getINode(-2).asDirectory()
           .replaceChild4ReferenceWithName(srcChild); 
-      withCount = (INodeReference.WithCount)withName.getReferredINode();
+      withCount = (INodeReference.WithCount) withName.getReferredINode();
       srcChild = withName;
       srcIIP.setLastINode(srcChild);
+    } else if (srcChildIsReference) {
+      // srcChild is reference but srcChild is not in latest snapshot
+      withCount = (WithCount) srcChild.asReference().getReferredINode();
     } else {
       withCount = null;
     }
@@ -602,7 +608,6 @@ public class FSDirectory implements Closeable {
         return false;
       }
       
-      // add src to the destination
       if (dstParent.getParent() == null) {
         // src and dst file/dir are in the same directory, and the dstParent has
         // been replaced when we removed the src. Refresh the dstIIP and
@@ -611,6 +616,8 @@ public class FSDirectory implements Closeable {
         dstParent = dstIIP.getINode(-2);
       }
       
+      // add src to the destination
+      
       srcChild = srcIIP.getLastINode();
       final byte[] dstChildName = dstIIP.getLastLocalName();
       final INode toDst;
@@ -645,17 +652,29 @@ public class FSDirectory implements Closeable {
       }
     } finally {
       if (!added) {
+        final INodeDirectory srcParent = srcIIP.getINode(-2).asDirectory();
+        final INode oldSrcChild = srcChild;
         // put it back
         if (withCount == null) {
           srcChild.setLocalName(srcChildName);
         } else if (!srcChildIsReference) { // src must be in snapshot
-          final INodeDirectoryWithSnapshot srcParent = 
-              (INodeDirectoryWithSnapshot) srcIIP.getINode(-2).asDirectory();
           final INode originalChild = withCount.getReferredINode();
-          srcParent.replaceRemovedChild(srcChild, originalChild);
           srcChild = originalChild;
+        } else {
+          final INodeReference originalRef = new INodeReference.DstReference(
+              srcParent, withCount, srcRefDstSnapshot);
+          withCount.setParentReference(originalRef);
+          srcChild = originalRef;
+        }
+        
+        if (isSrcInSnapshot) {
+          ((INodeDirectoryWithSnapshot) srcParent).undoRename4ScrParent(
+              oldSrcChild.asReference(), srcChild, srcIIP.getLatestSnapshot());
+        } else {
+          // srcParent is not an INodeDirectoryWithSnapshot, we only need to add
+          // the srcChild back
+          addLastINodeNoQuotaCheck(srcIIP, srcChild);
         }
-        addLastINodeNoQuotaCheck(srcIIP, srcChild);
       }
     }
     NameNode.stateChangeLog.warn("DIR* FSDirectory.unprotectedRenameTo: "
@@ -797,12 +816,17 @@ public class FSDirectory implements Closeable {
     
     // check srcChild for reference
     final INodeReference.WithCount withCount;
-    if (srcChildIsReference || isSrcInSnapshot) {
+    int srcRefDstSnapshot = srcChildIsReference ? srcChild.asReference()
+        .getDstSnapshotId() : Snapshot.INVALID_ID;
+    if (isSrcInSnapshot) {
       final INodeReference.WithName withName = srcIIP.getINode(-2).asDirectory()
           .replaceChild4ReferenceWithName(srcChild); 
-      withCount = (INodeReference.WithCount)withName.getReferredINode();
+      withCount = (INodeReference.WithCount) withName.getReferredINode();
       srcChild = withName;
       srcIIP.setLastINode(srcChild);
+    } else if (srcChildIsReference) {
+      // srcChild is reference but srcChild is not in latest snapshot
+      withCount = (WithCount) srcChild.asReference().getReferredINode();
     } else {
       withCount = null;
     }
@@ -888,21 +912,38 @@ public class FSDirectory implements Closeable {
     } finally {
       if (undoRemoveSrc) {
         // Rename failed - restore src
-        srcChild = srcIIP.getLastINode();
+        final INodeDirectory srcParent = srcIIP.getINode(-2).asDirectory();
+        final INode oldSrcChild = srcChild;
+        // put it back
         if (withCount == null) {
           srcChild.setLocalName(srcChildName);
         } else if (!srcChildIsReference) { // src must be in snapshot
-          final INodeDirectoryWithSnapshot srcParent
-              = (INodeDirectoryWithSnapshot)srcIIP.getINode(-2).asDirectory();
           final INode originalChild = withCount.getReferredINode();
-          srcParent.replaceRemovedChild(srcChild, originalChild);
           srcChild = originalChild;
+        } else {
+          final INodeReference originalRef = new INodeReference.DstReference(
+              srcParent, withCount, srcRefDstSnapshot);
+          withCount.setParentReference(originalRef);
+          srcChild = originalRef;
+        }
+        
+        if (srcParent instanceof INodeDirectoryWithSnapshot) {
+          ((INodeDirectoryWithSnapshot) srcParent).undoRename4ScrParent(
+              oldSrcChild.asReference(), srcChild, srcIIP.getLatestSnapshot());
+        } else {
+          // srcParent is not an INodeDirectoryWithSnapshot, we only need to add
+          // the srcChild back
+          addLastINodeNoQuotaCheck(srcIIP, srcChild);
         }
-        addLastINodeNoQuotaCheck(srcIIP, srcChild);
       }
       if (undoRemoveDst) {
         // Rename failed - restore dst
-        addLastINodeNoQuotaCheck(dstIIP, removedDst);
+        if (dstParent instanceof INodeDirectoryWithSnapshot) {
+          ((INodeDirectoryWithSnapshot) dstParent).undoRename4DstParent(
+              removedDst, dstIIP.getLatestSnapshot());
+        } else {
+          addLastINodeNoQuotaCheck(dstIIP, removedDst);
+        }
       }
     }
     NameNode.stateChangeLog.warn("DIR* FSDirectory.unprotectedRenameTo: "
@@ -1270,7 +1311,7 @@ public class FSDirectory implements Closeable {
       Quota.Counts counts = targetNode.cleanSubtree(null, latestSnapshot,
           collectedBlocks);
       parent.addSpaceConsumed(-counts.get(Quota.NAMESPACE),
-          -counts.get(Quota.DISKSPACE));
+          -counts.get(Quota.DISKSPACE), true);
       removed = counts.get(Quota.NAMESPACE);
     }
     if (NameNode.stateChangeLog.isDebugEnabled()) {

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INode.java

@@ -376,11 +376,11 @@ public abstract class INode implements Diff.Element<byte[]> {
    * Check and add namespace/diskspace consumed to itself and the ancestors.
    * @throws QuotaExceededException if quote is violated.
    */
-  public void addSpaceConsumed(long nsDelta, long dsDelta)
+  public void addSpaceConsumed(long nsDelta, long dsDelta, boolean verify)
       throws QuotaExceededException {
     final INodeDirectory parentDir = getParent();
     if (parentDir != null) {
-      parentDir.addSpaceConsumed(nsDelta, dsDelta);
+      parentDir.addSpaceConsumed(nsDelta, dsDelta, verify);
     }
   }
 
@@ -403,7 +403,7 @@ public abstract class INode implements Diff.Element<byte[]> {
   /**
    * Count subtree {@link Quota#NAMESPACE} and {@link Quota#DISKSPACE} usages.
    */
-  final Quota.Counts computeQuotaUsage() {
+  public final Quota.Counts computeQuotaUsage() {
     return computeQuotaUsage(new Quota.Counts(), true);
   }
 

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectory.java

@@ -216,6 +216,7 @@ public class INodeDirectory extends INodeWithAdditionalFields {
     Preconditions.checkState(i >= 0);
     Preconditions.checkState(oldChild == children.get(i));
     
+    // TODO: the first case may never be hit
     if (oldChild.isReference() && !newChild.isReference()) {
       final INode withCount = oldChild.asReference().getReferredINode();
       withCount.asReference().setReferredINode(newChild);

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeDirectoryWithQuota.java

@@ -140,21 +140,23 @@ public class INodeDirectoryWithQuota extends INodeDirectory {
   }
   
   @Override
-  public final void addSpaceConsumed(final long nsDelta, final long dsDelta)
-      throws QuotaExceededException {
+  public final void addSpaceConsumed(final long nsDelta, final long dsDelta,
+      boolean verify) throws QuotaExceededException {
     if (isQuotaSet()) { 
       // The following steps are important: 
       // check quotas in this inode and all ancestors before changing counts
       // so that no change is made if there is any quota violation.
 
-      // (1) verify quota in this inode  
-      verifyQuota(nsDelta, dsDelta);
+      // (1) verify quota in this inode
+      if (verify) {
+        verifyQuota(nsDelta, dsDelta);
+      }
       // (2) verify quota and then add count in ancestors 
-      super.addSpaceConsumed(nsDelta, dsDelta);
+      super.addSpaceConsumed(nsDelta, dsDelta, verify);
       // (3) add count in this inode
       addSpaceConsumed2Cache(nsDelta, dsDelta);
     } else {
-      super.addSpaceConsumed(nsDelta, dsDelta);
+      super.addSpaceConsumed(nsDelta, dsDelta, verify);
     }
   }
   

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodeReference.java

@@ -254,9 +254,9 @@ public abstract class INodeReference extends INode {
   }
 
   @Override
-  public final void addSpaceConsumed(long nsDelta, long dsDelta
-      ) throws QuotaExceededException {
-    referred.addSpaceConsumed(nsDelta, dsDelta);
+  public final void addSpaceConsumed(long nsDelta, long dsDelta, boolean verify)
+      throws QuotaExceededException {
+    referred.addSpaceConsumed(nsDelta, dsDelta, verify);
   }
 
   @Override

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/snapshot/AbstractINodeDiffList.java

@@ -108,7 +108,7 @@ abstract class AbstractINodeDiffList<N extends INode,
   /** Add an {@link AbstractINodeDiff} for the given snapshot. */
   final D addDiff(Snapshot latest, N currentINode)
       throws QuotaExceededException {
-    currentINode.addSpaceConsumed(1, 0);
+    currentINode.addSpaceConsumed(1, 0, true);
     return addLast(factory.createDiff(latest, currentINode));
   }
 

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/snapshot/INodeDirectorySnapshottable.java

@@ -325,7 +325,7 @@ public class INodeDirectorySnapshottable extends INodeDirectoryWithSnapshot {
         INodeDirectory parent = getParent();
         if (parent != null) {
           parent.addSpaceConsumed(-counts.get(Quota.NAMESPACE),
-              -counts.get(Quota.DISKSPACE));
+              -counts.get(Quota.DISKSPACE), true);
         }
       } catch(QuotaExceededException e) {
         LOG.error("BUG: removeSnapshot increases namespace usage.", e);

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/snapshot/INodeDirectoryWithSnapshot.java

@@ -81,16 +81,16 @@ public class INodeDirectoryWithSnapshot extends INodeDirectoryWithQuota {
       return true;
     }
 
-    private final boolean removeCreatedChild(final int c, final INode child) {
-      final List<INode> created = getList(ListType.CREATED);
-      if (created.get(c) == child) {
-        final INode removed = created.remove(c);
-        Preconditions.checkState(removed == child);
+    private final boolean removeChild(ListType type, final INode child) {
+      final List<INode> list = getList(type);
+      final int i = searchIndex(type, child.getLocalNameBytes());
+      if (i >= 0 && list.get(i) == child) {
+        list.remove(i);
         return true;
       }
       return false;
     }
-
+    
     /** clear the created list */
     private Quota.Counts destroyCreatedList(
         final INodeDirectoryWithSnapshot currentINode,
@@ -452,6 +452,18 @@ public class INodeDirectoryWithSnapshot extends INodeDirectoryWithQuota {
       }
       return false;
     }
+    
+    /** Remove the given child in the created/deleted list, if there is any. */
+    private boolean removeChild(final ListType type, final INode child) {
+      final List<DirectoryDiff> diffList = asList();
+      for(int i = diffList.size() - 1; i >= 0; i--) {
+        final ChildrenDiff diff = diffList.get(i).diff;
+        if (diff.removeChild(type, child)) {
+          return true;
+        }
+      }
+      return false;
+    }
   }
 
   /**
@@ -627,15 +639,11 @@ public class INodeDirectoryWithSnapshot extends INodeDirectoryWithQuota {
     }
 
     // remove same child from the created list, if there is any.
-    final byte[] name = child.getLocalNameBytes();
     final List<DirectoryDiff> diffList = diffs.asList();
     for(int i = diffList.size() - 1; i >= 0; i--) {
       final ChildrenDiff diff = diffList.get(i).diff;
-      final int c = diff.searchIndex(ListType.CREATED, name);
-      if (c >= 0) {
-        if (diff.removeCreatedChild(c, child)) {
-          return true;
-        }
+      if (diff.removeChild(ListType.CREATED, child)) {
+        return true;
       }
     }
     return true;
@@ -646,12 +654,65 @@ public class INodeDirectoryWithSnapshot extends INodeDirectoryWithQuota {
     super.replaceChild(oldChild, newChild);
     diffs.replaceChild(ListType.CREATED, oldChild, newChild);
   }
-
-  /** The child just has been removed, replace it with a reference. */
-  public void replaceRemovedChild(INode oldChild, INode newChild) {
-    // the old child must be in the deleted list
-    Preconditions.checkState(
-        diffs.replaceChild(ListType.DELETED, oldChild, newChild));
+  
+  /**
+   * This method is usually called by the undo section of rename.
+   * 
+   * Before calling this function, in the rename operation, we replace the
+   * original src node (of the rename operation) with a reference node (WithName
+   * instance) in both the children list and a created list, delete the
+   * reference node from the children list, and add it to the corresponding
+   * deleted list.
+   * 
+   * To undo the above operations, we have the following steps in particular:
+   * 
+   * <pre>
+   * 1) remove the WithName node from the deleted list (if it exists) 
+   * 2) replace the WithName node in the created list with srcChild 
+   * 3) add srcChild back as a child of srcParent. Note that we already add 
+   * the node into the created list of a snapshot diff in step 2, we do not need
+   * to add srcChild to the created list of the latest snapshot.
+   * </pre>
+   * 
+   * We do not need to update quota usage because the old child is in the 
+   * deleted list before. 
+   * 
+   * @param oldChild
+   *          The reference node to be removed/replaced
+   * @param newChild
+   *          The node to be added back
+   * @param latestSnapshot
+   *          The latest snapshot. Note this may not be the last snapshot in the
+   *          {@link #diffs}, since the src tree of the current rename operation
+   *          may be the dst tree of a previous rename.
+   * @throws QuotaExceededException should not throw this exception
+   */
+  public void undoRename4ScrParent(final INodeReference oldChild,
+      final INode newChild, Snapshot latestSnapshot)
+      throws QuotaExceededException {
+    diffs.removeChild(ListType.DELETED, oldChild);
+    diffs.replaceChild(ListType.CREATED, oldChild, newChild);
+    addChild(newChild, true, null);
+  }
+  
+  /**
+   * Undo the rename operation for the dst tree, i.e., if the rename operation
+   * (with OVERWRITE option) removes a file/dir from the dst tree, add it back
+   * and delete possible record in the deleted list.  
+   */
+  public void undoRename4DstParent(final INode deletedChild,
+      Snapshot latestSnapshot) throws QuotaExceededException {
+    boolean removeDeletedChild = diffs.removeChild(ListType.DELETED,
+        deletedChild);
+    final boolean added = addChild(deletedChild, true, removeDeletedChild ? null
+        : latestSnapshot);
+    // update quota usage if adding is successfully and the old child has not
+    // been stored in deleted list before
+    if (added && !removeDeletedChild) {
+      final Quota.Counts counts = deletedChild.computeQuotaUsage();
+      addSpaceConsumed(counts.get(Quota.NAMESPACE),
+          counts.get(Quota.DISKSPACE), false);
+    }
   }
 
   @Override

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/snapshot/TestRenameWithSnapshots.java

@@ -21,6 +21,10 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
+import static org.mockito.Matchers.anyBoolean;
+import static org.mockito.Matchers.anyObject;
+import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.spy;
 
 import java.io.File;
 import java.io.IOException;
@@ -48,7 +52,10 @@ import org.apache.hadoop.hdfs.server.namenode.INodeDirectory;
 import org.apache.hadoop.hdfs.server.namenode.INodeReference;
 import org.apache.hadoop.hdfs.server.namenode.INodeReference.WithCount;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.FileWithSnapshot.FileDiff;
+import org.apache.hadoop.hdfs.server.namenode.snapshot.INodeDirectoryWithSnapshot.ChildrenDiff;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.INodeDirectoryWithSnapshot.DirectoryDiff;
+import org.apache.hadoop.hdfs.util.Diff.ListType;
+import org.apache.hadoop.hdfs.util.ReadOnlyList;
 import org.apache.hadoop.test.GenericTestUtils;
 import org.junit.After;
 import org.junit.Assert;
@@ -1159,4 +1166,224 @@ public class TestRenameWithSnapshots {
     hdfs.deleteSnapshot(sdir1, "s1");
     restartClusterAndCheckImage();
   }
+  
+  /**
+   * Test the undo section of rename. Before the rename, we create the renamed 
+   * file/dir before taking the snapshot.
+   */
+  @Test
+  public void testRenameUndo() throws Exception {
+    final Path sdir1 = new Path("/dir1");
+    final Path sdir2 = new Path("/dir2");
+    hdfs.mkdirs(sdir1);
+    hdfs.mkdirs(sdir2);
+    final Path foo = new Path(sdir1, "foo");
+    final Path bar = new Path(foo, "bar");
+    DFSTestUtil.createFile(hdfs, bar, BLOCKSIZE, REPL, SEED);
+    final Path dir2file = new Path(sdir2, "file");
+    DFSTestUtil.createFile(hdfs, dir2file, BLOCKSIZE, REPL, SEED);
+    
+    SnapshotTestHelper.createSnapshot(hdfs, sdir1, "s1");
+    
+    INodeDirectory dir2 = fsdir.getINode4Write(sdir2.toString()).asDirectory();
+    INodeDirectory mockDir2 = spy(dir2);
+    doReturn(false).when(mockDir2).addChild((INode) anyObject(), anyBoolean(),
+            (Snapshot) anyObject());
+    INodeDirectory root = fsdir.getINode4Write("/").asDirectory();
+    root.replaceChild(dir2, mockDir2);
+    
+    final Path newfoo = new Path(sdir2, "foo");
+    boolean result = hdfs.rename(foo, newfoo);
+    assertFalse(result);
+    
+    // check the current internal details
+    INodeDirectorySnapshottable dir1Node = (INodeDirectorySnapshottable) fsdir
+        .getINode4Write(sdir1.toString());
+    ReadOnlyList<INode> dir1Children = dir1Node.getChildrenList(null);
+    assertEquals(1, dir1Children.size());
+    assertEquals(foo.getName(), dir1Children.get(0).getLocalName());
+    List<DirectoryDiff> dir1Diffs = dir1Node.getDiffs().asList();
+    assertEquals(1, dir1Diffs.size());
+    assertEquals("s1", dir1Diffs.get(0).snapshot.getRoot().getLocalName());
+    
+    // after the undo of rename, both the created and deleted list of sdir1
+    // should be empty
+    ChildrenDiff childrenDiff = dir1Diffs.get(0).getChildrenDiff();
+    assertEquals(0, childrenDiff.getList(ListType.DELETED).size());
+    assertEquals(0, childrenDiff.getList(ListType.CREATED).size());
+    
+    INode fooNode = fsdir.getINode4Write(foo.toString());
+    assertTrue(fooNode instanceof INodeDirectoryWithSnapshot);
+    List<DirectoryDiff> fooDiffs = ((INodeDirectoryWithSnapshot) fooNode)
+        .getDiffs().asList();
+    assertEquals(1, fooDiffs.size());
+    assertEquals("s1", fooDiffs.get(0).snapshot.getRoot().getLocalName());
+    
+    final Path foo_s1 = SnapshotTestHelper.getSnapshotPath(sdir1, "s1", "foo");
+    INode fooNode_s1 = fsdir.getINode(foo_s1.toString());
+    assertTrue(fooNode_s1 == fooNode);
+    
+    // check sdir2
+    assertFalse(hdfs.exists(newfoo));
+    INodeDirectory dir2Node = fsdir.getINode4Write(sdir2.toString())
+        .asDirectory();
+    assertFalse(dir2Node instanceof INodeDirectoryWithSnapshot);
+    ReadOnlyList<INode> dir2Children = dir2Node.getChildrenList(null);
+    assertEquals(1, dir2Children.size());
+    assertEquals(dir2file.getName(), dir2Children.get(0).getLocalName());
+  }
+
+  /**
+   * Test the undo section of rename. Before the rename, we create the renamed 
+   * file/dir after taking the snapshot.
+   */
+  @Test
+  public void testRenameUndo_2() throws Exception {
+    final Path sdir1 = new Path("/dir1");
+    final Path sdir2 = new Path("/dir2");
+    hdfs.mkdirs(sdir1);
+    hdfs.mkdirs(sdir2);
+    final Path dir2file = new Path(sdir2, "file");
+    DFSTestUtil.createFile(hdfs, dir2file, BLOCKSIZE, REPL, SEED);
+    
+    SnapshotTestHelper.createSnapshot(hdfs, sdir1, "s1");
+    
+    // create foo after taking snapshot
+    final Path foo = new Path(sdir1, "foo");
+    final Path bar = new Path(foo, "bar");
+    DFSTestUtil.createFile(hdfs, bar, BLOCKSIZE, REPL, SEED);
+    
+    INodeDirectory dir2 = fsdir.getINode4Write(sdir2.toString()).asDirectory();
+    INodeDirectory mockDir2 = spy(dir2);
+    doReturn(false).when(mockDir2).addChild((INode) anyObject(), anyBoolean(),
+            (Snapshot) anyObject());
+    INodeDirectory root = fsdir.getINode4Write("/").asDirectory();
+    root.replaceChild(dir2, mockDir2);
+    
+    final Path newfoo = new Path(sdir2, "foo");
+    boolean result = hdfs.rename(foo, newfoo);
+    assertFalse(result);
+    
+    // check the current internal details
+    INodeDirectorySnapshottable dir1Node = (INodeDirectorySnapshottable) fsdir
+        .getINode4Write(sdir1.toString());
+    ReadOnlyList<INode> dir1Children = dir1Node.getChildrenList(null);
+    assertEquals(1, dir1Children.size());
+    assertEquals(foo.getName(), dir1Children.get(0).getLocalName());
+    List<DirectoryDiff> dir1Diffs = dir1Node.getDiffs().asList();
+    assertEquals(1, dir1Diffs.size());
+    assertEquals("s1", dir1Diffs.get(0).snapshot.getRoot().getLocalName());
+    
+    // after the undo of rename, the created list of sdir1 should contain 
+    // 1 element
+    ChildrenDiff childrenDiff = dir1Diffs.get(0).getChildrenDiff();
+    assertEquals(0, childrenDiff.getList(ListType.DELETED).size());
+    assertEquals(1, childrenDiff.getList(ListType.CREATED).size());
+    
+    INode fooNode = fsdir.getINode4Write(foo.toString());
+    assertTrue(fooNode instanceof INodeDirectory);
+    assertTrue(childrenDiff.getList(ListType.CREATED).get(0) == fooNode);
+    
+    final Path foo_s1 = SnapshotTestHelper.getSnapshotPath(sdir1, "s1", "foo");
+    assertFalse(hdfs.exists(foo_s1));
+    
+    // check sdir2
+    assertFalse(hdfs.exists(newfoo));
+    INodeDirectory dir2Node = fsdir.getINode4Write(sdir2.toString())
+        .asDirectory();
+    assertFalse(dir2Node instanceof INodeDirectoryWithSnapshot);
+    ReadOnlyList<INode> dir2Children = dir2Node.getChildrenList(null);
+    assertEquals(1, dir2Children.size());
+    assertEquals(dir2file.getName(), dir2Children.get(0).getLocalName());
+  }
+  
+  /**
+   * Test the undo section of the second-time rename.
+   */
+  @Test
+  public void testRenameUndo_3() throws Exception {
+    final Path sdir1 = new Path("/dir1");
+    final Path sdir2 = new Path("/dir2");
+    final Path sdir3 = new Path("/dir3");
+    hdfs.mkdirs(sdir1);
+    hdfs.mkdirs(sdir2);
+    hdfs.mkdirs(sdir3);
+    final Path foo = new Path(sdir1, "foo");
+    final Path bar = new Path(foo, "bar");
+    DFSTestUtil.createFile(hdfs, bar, BLOCKSIZE, REPL, SEED);
+    
+    SnapshotTestHelper.createSnapshot(hdfs, sdir1, "s1");
+    SnapshotTestHelper.createSnapshot(hdfs, sdir2, "s2");
+    
+    INodeDirectory dir3 = fsdir.getINode4Write(sdir3.toString()).asDirectory();
+    INodeDirectory mockDir3 = spy(dir3);
+    doReturn(false).when(mockDir3).addChild((INode) anyObject(), anyBoolean(),
+            (Snapshot) anyObject());
+    INodeDirectory root = fsdir.getINode4Write("/").asDirectory();
+    root.replaceChild(dir3, mockDir3);
+    
+    final Path foo_dir2 = new Path(sdir2, "foo");
+    final Path foo_dir3 = new Path(sdir3, "foo");
+    hdfs.rename(foo, foo_dir2);
+    boolean result = hdfs.rename(foo_dir2, foo_dir3);
+    assertFalse(result);
+    
+    // check the current internal details
+    INodeDirectorySnapshottable dir2Node = (INodeDirectorySnapshottable) fsdir
+        .getINode4Write(sdir2.toString());
+    ReadOnlyList<INode> dir2Children = dir2Node.getChildrenList(null);
+    assertEquals(1, dir2Children.size());
+    List<DirectoryDiff> dir2Diffs = dir2Node.getDiffs().asList();
+    assertEquals(1, dir2Diffs.size());
+    assertEquals("s2", Snapshot.getSnapshotName(dir2Diffs.get(0).snapshot));
+    ChildrenDiff childrenDiff = dir2Diffs.get(0).getChildrenDiff();
+    assertEquals(0, childrenDiff.getList(ListType.DELETED).size());
+    assertEquals(1, childrenDiff.getList(ListType.CREATED).size());
+    final Path foo_s2 = SnapshotTestHelper.getSnapshotPath(sdir2, "s2", "foo");
+    assertFalse(hdfs.exists(foo_s2));
+    
+    INode fooNode = fsdir.getINode4Write(foo_dir2.toString());
+    assertTrue(childrenDiff.getList(ListType.CREATED).get(0) == fooNode);
+    assertTrue(fooNode instanceof INodeReference.DstReference);
+    List<DirectoryDiff> fooDiffs = ((INodeDirectoryWithSnapshot) fooNode
+        .asDirectory()).getDiffs().asList();
+    assertEquals(1, fooDiffs.size());
+    assertEquals("s1", fooDiffs.get(0).snapshot.getRoot().getLocalName());
+    
+    // create snapshot on sdir2 and rename again
+    hdfs.createSnapshot(sdir2, "s3");
+    result = hdfs.rename(foo_dir2, foo_dir3);
+    assertFalse(result);
+
+    // check internal details again
+    dir2Node = (INodeDirectorySnapshottable) fsdir.getINode4Write(sdir2
+        .toString());
+    fooNode = fsdir.getINode4Write(foo_dir2.toString());
+    dir2Children = dir2Node.getChildrenList(null);
+    assertEquals(1, dir2Children.size());
+    dir2Diffs = dir2Node.getDiffs().asList();
+    assertEquals(2, dir2Diffs.size());
+    assertEquals("s2", Snapshot.getSnapshotName(dir2Diffs.get(0).snapshot));
+    assertEquals("s3", Snapshot.getSnapshotName(dir2Diffs.get(1).snapshot));
+    
+    childrenDiff = dir2Diffs.get(0).getChildrenDiff();
+    assertEquals(0, childrenDiff.getList(ListType.DELETED).size());
+    assertEquals(1, childrenDiff.getList(ListType.CREATED).size());
+    assertTrue(childrenDiff.getList(ListType.CREATED).get(0) == fooNode);
+    
+    childrenDiff = dir2Diffs.get(1).getChildrenDiff();
+    assertEquals(0, childrenDiff.getList(ListType.DELETED).size());
+    assertEquals(0, childrenDiff.getList(ListType.CREATED).size());
+    
+    final Path foo_s3 = SnapshotTestHelper.getSnapshotPath(sdir2, "s3", "foo");
+    assertFalse(hdfs.exists(foo_s2));
+    assertTrue(hdfs.exists(foo_s3));
+    
+    assertTrue(fooNode instanceof INodeReference.DstReference);
+    fooDiffs = ((INodeDirectoryWithSnapshot) fooNode.asDirectory()).getDiffs()
+        .asList();
+    assertEquals(2, fooDiffs.size());
+    assertEquals("s1", fooDiffs.get(0).snapshot.getRoot().getLocalName());
+    assertEquals("s3", fooDiffs.get(1).snapshot.getRoot().getLocalName());
+  }
 }