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From a..@apache.org
Subject [2/2] git commit: HDFS-6931. Move lazily persisted replicas to finalized directory on DN startup. (Arpit Agarwal)
Date Fri, 29 Aug 2014 06:15:36 GMT
HDFS-6931. Move lazily persisted replicas to finalized directory on DN startup. (Arpit Agarwal)


Project: http://git-wip-us.apache.org/repos/asf/hadoop/repo
Commit: http://git-wip-us.apache.org/repos/asf/hadoop/commit/c92837ae
Tree: http://git-wip-us.apache.org/repos/asf/hadoop/tree/c92837ae
Diff: http://git-wip-us.apache.org/repos/asf/hadoop/diff/c92837ae

Branch: refs/heads/HDFS-6581
Commit: c92837aeab5188f6171d4016f91b3b4936a66beb
Parents: 4cf9afa
Author: arp <arp@apache.org>
Authored: Thu Aug 28 23:13:46 2014 -0700
Committer: arp <arp@apache.org>
Committed: Thu Aug 28 23:13:46 2014 -0700

----------------------------------------------------------------------
 .../hadoop-hdfs/CHANGES-HDFS-6581.txt           |   3 +
 .../datanode/fsdataset/impl/BlockPoolSlice.java | 168 ++++++++++++++++---
 .../datanode/fsdataset/impl/FsDatasetImpl.java  |   9 +-
 .../datanode/fsdataset/impl/FsVolumeImpl.java   |  12 +-
 .../datanode/fsdataset/impl/FsVolumeList.java   |  18 +-
 .../fsdataset/impl/TestLazyPersistFiles.java    |  53 +++++-
 6 files changed, 213 insertions(+), 50 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/hadoop/blob/c92837ae/hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-6581.txt
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-6581.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-6581.txt
index 881cb63..8791485 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-6581.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-6581.txt
@@ -27,3 +27,6 @@
     HDFS-6960. Bugfix in LazyWriter, fix test case and some refactoring.
     (Arpit Agarwal)
 
+    HDFS-6931. Move lazily persisted replicas to finalized directory on DN
+    startup. (Arpit Agarwal)
+

http://git-wip-us.apache.org/repos/asf/hadoop/blob/c92837ae/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/BlockPoolSlice.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/BlockPoolSlice.java
b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/BlockPoolSlice.java
index 1313fef..1bb6680 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/BlockPoolSlice.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/BlockPoolSlice.java
@@ -94,17 +94,6 @@ class BlockPoolSlice {
       }
     }
 
-    // Delete all checkpointed replicas on startup.
-    // TODO: We can move checkpointed replicas to the finalized dir and delete
-    //       the copy on RAM_DISK. For now we take the simpler approach.
-
-    FileUtil.fullyDelete(lazypersistDir);
-    if (!this.lazypersistDir.exists()) {
-      if (!this.lazypersistDir.mkdirs()) {
-        throw new IOException("Failed to mkdirs " + this.lazypersistDir);
-      }
-    }
-
     // Files that were being written when the datanode was last shutdown
     // are now moved back to the data directory. It is possible that
     // in the future, we might want to do some sort of datanode-local
@@ -271,6 +260,13 @@ class BlockPoolSlice {
     return blockFile;
   }
 
+  /**
+   * Save the given replica to persistent storage.
+   *
+   * @param replicaInfo
+   * @return The saved block file.
+   * @throws IOException
+   */
   File lazyPersistReplica(ReplicaInfo replicaInfo) throws IOException {
     if (!lazypersistDir.exists() && !lazypersistDir.mkdirs()) {
       FsDatasetImpl.LOG.warn("Failed to create " + lazypersistDir);
@@ -305,11 +301,21 @@ class BlockPoolSlice {
 
 
     
-  void getVolumeMap(ReplicaMap volumeMap) throws IOException {
+  void getVolumeMap(ReplicaMap volumeMap,
+                    final LazyWriteReplicaTracker lazyWriteReplicaMap)
+      throws IOException {
+    // Recover lazy persist replicas, they will be added to the volumeMap
+    // when we scan the finalized directory.
+    if (lazypersistDir.exists()) {
+      int numRecovered = moveLazyPersistReplicasToFinalized(lazypersistDir);
+      FsDatasetImpl.LOG.info(
+          "Recovered " + numRecovered + " replicas from " + lazypersistDir);
+    }
+
     // add finalized replicas
-    addToReplicasMap(volumeMap, finalizedDir, true);
+    addToReplicasMap(volumeMap, finalizedDir, lazyWriteReplicaMap, true);
     // add rbw replicas
-    addToReplicasMap(volumeMap, rbwDir, false);
+    addToReplicasMap(volumeMap, rbwDir, lazyWriteReplicaMap, false);
   }
 
   /**
@@ -338,18 +344,68 @@ class BlockPoolSlice {
 
 
   /**
+   * Move replicas in the lazy persist directory to their corresponding locations
+   * in the finalized directory.
+   * @return number of replicas recovered.
+   */
+  private int moveLazyPersistReplicasToFinalized(File source)
+      throws IOException {
+    File files[] = FileUtil.listFiles(source);
+    int numRecovered = 0;
+    for (File file : files) {
+      if (file.isDirectory()) {
+        numRecovered += moveLazyPersistReplicasToFinalized(file);
+      }
+
+      if (Block.isMetaFilename(file.getName())) {
+        File metaFile = file;
+        File blockFile = Block.metaToBlockFile(metaFile);
+        long blockId = Block.filename2id(blockFile.getName());
+        File targetDir = DatanodeUtil.idToBlockDir(finalizedDir, blockId);
+
+        if (blockFile.exists()) {
+          File targetBlockFile = new File(targetDir, blockFile.getName());
+          File targetMetaFile = new File(targetDir, metaFile.getName());
+
+          if (!targetDir.exists() && !targetDir.mkdirs()) {
+            FsDatasetImpl.LOG.warn("Failed to move " + blockFile + " to " + targetDir);
+            continue;
+          }
+
+          metaFile.renameTo(targetMetaFile);
+          blockFile.renameTo(targetBlockFile);
+
+          if (targetBlockFile.exists() && targetMetaFile.exists()) {
+            ++numRecovered;
+          } else {
+            // Failure should be rare.
+            FsDatasetImpl.LOG.warn("Failed to move " + blockFile + " to " + targetDir);
+          }
+        }
+      }
+    }
+
+    FileUtil.fullyDelete(source);
+    return numRecovered;
+  }
+
+  /**
    * Add replicas under the given directory to the volume map
    * @param volumeMap the replicas map
    * @param dir an input directory
+   * @param lazyWriteReplicaMap Map of replicas on transient
+   *                                storage.
    * @param isFinalized true if the directory has finalized replicas;
    *                    false if the directory has rbw replicas
    */
-  void addToReplicasMap(ReplicaMap volumeMap, File dir, boolean isFinalized
-      ) throws IOException {
+  void addToReplicasMap(ReplicaMap volumeMap, File dir,
+                        final LazyWriteReplicaTracker lazyWriteReplicaMap,
+                        boolean isFinalized)
+      throws IOException {
     File files[] = FileUtil.listFiles(dir);
     for (File file : files) {
       if (file.isDirectory()) {
-        addToReplicasMap(volumeMap, file, isFinalized);
+        addToReplicasMap(volumeMap, file, lazyWriteReplicaMap, isFinalized);
       }
 
       if (isFinalized && FsDatasetUtil.isUnlinkTmpFile(file)) {
@@ -405,13 +461,83 @@ class BlockPoolSlice {
         }
       }
 
-      ReplicaInfo oldReplica = volumeMap.add(bpid, newReplica);
-      if (oldReplica != null) {
-        FsDatasetImpl.LOG.warn("Two block files with the same block id exist " +
-            "on disk: " + oldReplica.getBlockFile() + " and " + file );
+      ReplicaInfo oldReplica = volumeMap.get(bpid, newReplica.getBlockId());
+      if (oldReplica == null) {
+        volumeMap.add(bpid, newReplica);
+      } else {
+        // We have multiple replicas of the same block so decide which one
+        // to keep.
+        newReplica = resolveDuplicateReplicas(newReplica, oldReplica, volumeMap);
+      }
+
+      // If we are retaining a replica on transient storage make sure
+      // it is in the lazyWriteReplicaMap so it can be persisted
+      // eventually.
+      if (newReplica.getVolume().isTransientStorage()) {
+        lazyWriteReplicaMap.addReplica(bpid, blockId, newReplica.getVolume());
+      } else {
+        lazyWriteReplicaMap.discardReplica(bpid, blockId, true);
       }
     }
   }
+
+  /**
+   * This method is invoked during DN startup when volumes are scanned to
+   * build up the volumeMap.
+   *
+   * Given two replicas, decide which one to keep. The preference is as
+   * follows:
+   *   1. Prefer the replica with the higher generation stamp.
+   *   2. If generation stamps are equal, prefer the replica with the
+   *      larger on-disk length.
+   *   3. If on-disk length is the same, prefer the replica on persistent
+   *      storage volume.
+   *   4. All other factors being equal, keep replica1.
+   *
+   * The other replica is removed from the volumeMap and is deleted from
+   * its storage volume.
+   *
+   * @param replica1
+   * @param replica2
+   * @param volumeMap
+   * @return the replica that is retained.
+   * @throws IOException
+   */
+  private ReplicaInfo resolveDuplicateReplicas(
+      final ReplicaInfo replica1, final ReplicaInfo replica2,
+      final ReplicaMap volumeMap) throws IOException {
+
+    ReplicaInfo replicaToKeep;
+    ReplicaInfo replicaToDelete;
+
+    if (replica1.getGenerationStamp() != replica2.getGenerationStamp()) {
+      replicaToKeep = replica1.getGenerationStamp() > replica2.getGenerationStamp()
+          ? replica1 : replica2;
+    } else if (replica1.getNumBytes() != replica2.getNumBytes()) {
+      replicaToKeep = replica1.getNumBytes() > replica2.getNumBytes() ?
+          replica1 : replica2;
+    } else if (replica1.getVolume().isTransientStorage() &&
+               !replica2.getVolume().isTransientStorage()) {
+      replicaToKeep = replica2;
+    } else {
+      replicaToKeep = replica1;
+    }
+
+    replicaToDelete = (replicaToKeep == replica1) ? replica2 : replica1;
+
+    // Update volumeMap.
+    volumeMap.add(bpid, replicaToKeep);
+
+    // Delete the files on disk. Failure here is okay.
+    replicaToDelete.getBlockFile().delete();
+    replicaToDelete.getMetaFile().delete();
+
+    FsDatasetImpl.LOG.info(
+        "resolveDuplicateReplicas keeping " + replicaToKeep.getBlockFile() +
+        ", deleting " + replicaToDelete.getBlockFile());
+
+    return replicaToKeep;
+  }
   
   /**
    * Find out the number of bytes in the block that match its crc.

http://git-wip-us.apache.org/repos/asf/hadoop/blob/c92837ae/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java
b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java
index 22f626c..10d98ad 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java
@@ -262,13 +262,13 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
     volumes = new FsVolumeList(volsFailed, blockChooserImpl);
     asyncDiskService = new FsDatasetAsyncDiskService(datanode);
 
-    // TODO: Initialize transientReplicaTracker from blocks on disk.
-
     for (int idx = 0; idx < storage.getNumStorageDirs(); idx++) {
       addVolume(dataLocations, storage.getStorageDir(idx));
     }
 
     cacheManager = new FsDatasetCache(this);
+
+    // Start the lazy writer once we have built the replica maps.
     lazyWriter = new Daemon(new LazyWriter(
         conf.getInt(DFSConfigKeys.DFS_DATANODE_LAZY_WRITER_INTERVAL_SEC,
                     DFSConfigKeys.DFS_DATANODE_LAZY_WRITER_INTERVAL_DEFAULT_SEC)));
@@ -287,7 +287,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
     // storageMap and asyncDiskService, consistent.
     FsVolumeImpl fsVolume = FsVolumeImplAllocator.createVolume(
         this, sd.getStorageUuid(), dir, this.conf, storageType);
-    fsVolume.getVolumeMap(volumeMap);
+    fsVolume.getVolumeMap(volumeMap, lazyWriteReplicaTracker);
 
     volumes.addVolume(fsVolume);
     storageMap.put(sd.getStorageUuid(),
@@ -2021,7 +2021,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
       volumes.addBlockPool(bpid, conf);
       volumeMap.initBlockPool(bpid);
     }
-    volumes.getAllVolumesMap(bpid, volumeMap);
+    volumes.getAllVolumesMap(bpid, volumeMap, lazyWriteReplicaTracker);
   }
 
   @Override
@@ -2261,6 +2261,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
         LOG.warn("Exception saving replica " + replicaState, ioe);
       } finally {
         if (!succeeded && replicaState != null) {
+          LOG.warn("Failed to save replica " + replicaState + ". re-enqueueing it.");
           lazyWriteReplicaTracker.reenqueueReplica(replicaState);
         }
       }

http://git-wip-us.apache.org/repos/asf/hadoop/blob/c92837ae/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeImpl.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeImpl.java
b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeImpl.java
index 85756b7..ccfb449 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeImpl.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeImpl.java
@@ -245,14 +245,18 @@ public class FsVolumeImpl implements FsVolumeSpi {
     }
   }
     
-  void getVolumeMap(ReplicaMap volumeMap) throws IOException {
+  void getVolumeMap(ReplicaMap volumeMap,
+                    final LazyWriteReplicaTracker lazyWriteReplicaMap)
+      throws IOException {
     for(BlockPoolSlice s : bpSlices.values()) {
-      s.getVolumeMap(volumeMap);
+      s.getVolumeMap(volumeMap, lazyWriteReplicaMap);
     }
   }
   
-  void getVolumeMap(String bpid, ReplicaMap volumeMap) throws IOException {
-    getBlockPoolSlice(bpid).getVolumeMap(volumeMap);
+  void getVolumeMap(String bpid, ReplicaMap volumeMap,
+                    final LazyWriteReplicaTracker lazyWriteReplicaMap)
+      throws IOException {
+    getBlockPoolSlice(bpid).getVolumeMap(volumeMap, lazyWriteReplicaMap);
   }
   
   @Override

http://git-wip-us.apache.org/repos/asf/hadoop/blob/c92837ae/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeList.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeList.java
b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeList.java
index f1b196a..67958bf 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeList.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsVolumeList.java
@@ -119,7 +119,10 @@ class FsVolumeList {
     return remaining;
   }
   
-  void getAllVolumesMap(final String bpid, final ReplicaMap volumeMap) throws IOException
{
+  void getAllVolumesMap(final String bpid,
+                        final ReplicaMap volumeMap,
+                        final LazyWriteReplicaTracker lazyWriteReplicaMap)
+      throws IOException {
     long totalStartTime = Time.monotonicNow();
     final List<IOException> exceptions = Collections.synchronizedList(
         new ArrayList<IOException>());
@@ -131,7 +134,7 @@ class FsVolumeList {
             FsDatasetImpl.LOG.info("Adding replicas to map for block pool " +
                 bpid + " on volume " + v + "...");
             long startTime = Time.monotonicNow();
-            v.getVolumeMap(bpid, volumeMap);
+            v.getVolumeMap(bpid, volumeMap, lazyWriteReplicaMap);
             long timeTaken = Time.monotonicNow() - startTime;
             FsDatasetImpl.LOG.info("Time to add replicas to map for block pool"
                 + " " + bpid + " on volume " + v + ": " + timeTaken + "ms");
@@ -160,17 +163,6 @@ class FsVolumeList {
         + totalTimeTaken + "ms");
   }
 
-  void getVolumeMap(String bpid, FsVolumeImpl volume, ReplicaMap volumeMap)
-      throws IOException {
-    FsDatasetImpl.LOG.info("Adding replicas to map for block pool " + bpid +
-                               " on volume " + volume + "...");
-    long startTime = Time.monotonicNow();
-    volume.getVolumeMap(bpid, volumeMap);
-    long timeTaken = Time.monotonicNow() - startTime;
-    FsDatasetImpl.LOG.info("Time to add replicas to map for block pool " + bpid +
-                               " on volume " + volume + ": " + timeTaken + "ms");
-  }
-    
   /**
    * Calls {@link FsVolumeImpl#checkDirs()} on each volume, removing any
    * volumes from the active list that result in a DiskErrorException.

http://git-wip-us.apache.org/repos/asf/hadoop/blob/c92837ae/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestLazyPersistFiles.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestLazyPersistFiles.java
b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestLazyPersistFiles.java
index af0e8ac..cac99a7 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestLazyPersistFiles.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestLazyPersistFiles.java
@@ -265,7 +265,9 @@ public class TestLazyPersistFiles {
     LocatedBlocks locatedBlocks = ensureFileReplicasOnStorageType(path, RAM_DISK);
 
     // Sleep for a short time to allow the lazy writer thread to do its job
-    Thread.sleep(3 * LAZY_WRITER_INTERVAL_SEC * 1000);
+    Thread.sleep(6 * LAZY_WRITER_INTERVAL_SEC * 1000);
+    
+    LOG.info("Verifying copy was saved to lazyPersist/");
 
     // Make sure that there is a saved copy of the replica on persistent
     // storage.
@@ -330,23 +332,52 @@ public class TestLazyPersistFiles {
     ensureFileReplicasOnStorageType(path1, DEFAULT);
   }
 
-  /**
-   * TODO: Stub test, to be completed.
-   * Verify that checksum computation is skipped for files written to memory.
-   */
   @Test (timeout=300000)
-  public void testChecksumIsSkipped()
+  public void testDnRestartWithSavedReplicas()
       throws IOException, InterruptedException {
+
     startUpCluster(REPL_FACTOR,
-                   new StorageType[] {RAM_DISK, DEFAULT }, -1);
+        new StorageType[] {RAM_DISK, DEFAULT },
+        (2 * BLOCK_SIZE - 1));     // 1 replica + delta.
     final String METHOD_NAME = GenericTestUtils.getMethodName();
     Path path1 = new Path("/" + METHOD_NAME + ".01.dat");
 
     makeTestFile(path1, BLOCK_SIZE, true);
     ensureFileReplicasOnStorageType(path1, RAM_DISK);
 
-    // Verify checksum was not computed.
+    // Sleep for a short time to allow the lazy writer thread to do its job.
+    // However the block replica should not be evicted from RAM_DISK yet.
+    Thread.sleep(3 * LAZY_WRITER_INTERVAL_SEC * 1000);
+    ensureFileReplicasOnStorageType(path1, RAM_DISK);
 
+    LOG.info("Restarting the DataNode");
+    cluster.restartDataNode(0, true);
+    cluster.waitActive();
+
+    // Ensure that the replica is now on persistent storage.
+    ensureFileReplicasOnStorageType(path1, DEFAULT);
+  }
+
+  @Test (timeout=300000)
+  public void testDnRestartWithUnsavedReplicas()
+      throws IOException, InterruptedException {
+
+    startUpCluster(REPL_FACTOR,
+                   new StorageType[] {RAM_DISK, DEFAULT },
+                   (2 * BLOCK_SIZE - 1));     // 1 replica + delta.
+    stopLazyWriter(cluster.getDataNodes().get(0));
+
+    final String METHOD_NAME = GenericTestUtils.getMethodName();
+    Path path1 = new Path("/" + METHOD_NAME + ".01.dat");
+    makeTestFile(path1, BLOCK_SIZE, true);
+    ensureFileReplicasOnStorageType(path1, RAM_DISK);
+
+    LOG.info("Restarting the DataNode");
+    cluster.restartDataNode(0, true);
+    cluster.waitActive();
+
+    // Ensure that the replica is still on transient storage.
+    ensureFileReplicasOnStorageType(path1, RAM_DISK);
   }
 
   // ---- Utility functions for all test cases -------------------------------
@@ -443,4 +474,10 @@ public class TestLazyPersistFiles {
 
     return locatedBlocks;
   }
+
+  private void stopLazyWriter(DataNode dn) {
+    // Stop the lazyWriter daemon.
+    FsDatasetImpl fsDataset = ((FsDatasetImpl) dn.getFSDataset());
+    ((FsDatasetImpl.LazyWriter) fsDataset.lazyWriter.getRunnable()).stop();
+  }
 }


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