HDFS-15574. Remove unnecessary sort of block list in DirectoryScanner. Contributed by Stephen O'Donnell.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DirectoryScanner.java

@@ -482,8 +482,7 @@ public class DirectoryScanner implements Runnable {
         Collection<ScanInfo> diffRecord = new ArrayList<>();
 
         statsRecord.totalBlocks = blockpoolReport.size();
-        final List<ReplicaInfo> bl = dataset.getFinalizedBlocks(bpid);
+        final List<ReplicaInfo> bl = dataset.getSortedFinalizedBlocks(bpid);
-        Collections.sort(bl); // Sort based on blockId
 
         int d = 0; // index for blockpoolReport
         int m = 0; // index for memReprot

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsDatasetSpi.java

@@ -237,16 +237,17 @@ public interface FsDatasetSpi<V extends FsVolumeSpi> extends FSDatasetMBean {
   VolumeFailureSummary getVolumeFailureSummary();
 
   /**
-   * Gets a list of references to the finalized blocks for the given block pool.
+   * Gets a sorted list of references to the finalized blocks for the given
+   * block pool. The list is sorted by blockID.
    * <p>
    * Callers of this function should call
    * {@link FsDatasetSpi#acquireDatasetLock} to avoid blocks' status being
    * changed during list iteration.
    * </p>
    * @return a list of references to the finalized blocks for the given block
-   *         pool.
+   *         pool. The list is sorted by blockID.
    */
-  List<ReplicaInfo> getFinalizedBlocks(String bpid);
+  List<ReplicaInfo> getSortedFinalizedBlocks(String bpid);
 
   /**
    * Check whether the in-memory block record matches the block on the disk,

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java

@@ -1992,17 +1992,18 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
   }
 
   /**
-   * Gets a list of references to the finalized blocks for the given block pool.
+   * Gets a list of references to the finalized blocks for the given block pool,
+   * sorted by blockID.
    * <p>
    * Callers of this function should call
    * {@link FsDatasetSpi#acquireDatasetLock()} to avoid blocks' status being
    * changed during list iteration.
    * </p>
    * @return a list of references to the finalized blocks for the given block
-   *         pool.
+   *         pool. The list is sorted by blockID.
    */
   @Override
-  public List<ReplicaInfo> getFinalizedBlocks(String bpid) {
+  public List<ReplicaInfo> getSortedFinalizedBlocks(String bpid) {
     try (AutoCloseableLock lock = datasetReadLock.acquire()) {
       final List<ReplicaInfo> finalized = new ArrayList<ReplicaInfo>(
           volumeMap.size(bpid));

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestCrcCorruption.java

@@ -173,7 +173,7 @@ public class TestCrcCorruption {
       final DataNode dn = cluster.getDataNodes().get(dnIdx);
       final String bpid = cluster.getNamesystem().getBlockPoolId();
       List<ReplicaInfo> replicas =
-          dn.getFSDataset().getFinalizedBlocks(bpid);
+          dn.getFSDataset().getSortedFinalizedBlocks(bpid);
       assertTrue("Replicas do not exist", !replicas.isEmpty());
 
       for (int idx = 0; idx < replicas.size(); idx++) {

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestReconstructStripedFile.java

@@ -540,7 +540,7 @@ public class TestReconstructStripedFile {
     writeFile(fs, "/ec-xmits-weight", fileLen);
 
     DataNode dn = cluster.getDataNodes().get(0);
-    int corruptBlocks = dn.getFSDataset().getFinalizedBlocks(
+    int corruptBlocks = dn.getFSDataset().getSortedFinalizedBlocks(
         cluster.getNameNode().getNamesystem().getBlockPoolId()).size();
     int expectedXmits = corruptBlocks * expectedWeight;
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/SimulatedFSDataset.java

@@ -1510,7 +1510,7 @@ public class SimulatedFSDataset implements FsDatasetSpi<FsVolumeSpi> {
   }
 
   @Override
-  public List<ReplicaInfo> getFinalizedBlocks(String bpid) {
+  public List<ReplicaInfo> getSortedFinalizedBlocks(String bpid) {
     throw new UnsupportedOperationException();
   }
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalDatasetImpl.java

@@ -90,7 +90,7 @@ public class ExternalDatasetImpl implements FsDatasetSpi<ExternalVolumeImpl> {
   }
 
   @Override
-  public List<ReplicaInfo> getFinalizedBlocks(String bpid) {
+  public List<ReplicaInfo> getSortedFinalizedBlocks(String bpid) {
     return null;
   }
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestFsDatasetImpl.java

@@ -80,6 +80,7 @@ import java.io.OutputStreamWriter;
 import java.io.Writer;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
+import java.util.Random;
 import java.util.concurrent.CountDownLatch;
 import java.util.HashSet;
 import java.util.List;
@@ -570,6 +571,41 @@ public class TestFsDatasetImpl {
     FsDatasetTestUtil.assertFileLockReleased(badDir.toString());
   }
 
+  @Test
+  /**
+   * This test is here primarily to catch any case where the datanode replica
+   * map structure is changed to a new structure which is not sorted and hence
+   * reading the blocks from it directly would not be sorted.
+   */
+  public void testSortedFinalizedBlocksAreSorted() throws IOException {
+    this.conf = new HdfsConfiguration();
+    MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).build();
+    try {
+      cluster.waitActive();
+      DataNode dn = cluster.getDataNodes().get(0);
+
+      FsDatasetSpi<?> ds = DataNodeTestUtils.getFSDataset(dn);
+      ds.addBlockPool(BLOCKPOOL, conf);
+
+      // Load 1000 blocks with random blockIDs
+      for (int i=0; i<=1000; i++) {
+        ExtendedBlock eb = new ExtendedBlock(
+            BLOCKPOOL, new Random().nextInt(), 1000, 1000 + i);
+        cluster.getFsDatasetTestUtils(0).createFinalizedReplica(eb);
+      }
+      // Get the sorted blocks and validate the arrayList is sorted
+      List<ReplicaInfo> replicaList = ds.getSortedFinalizedBlocks(BLOCKPOOL);
+      for (int i=0; i<replicaList.size() - 1; i++) {
+        if (replicaList.get(i).compareTo(replicaList.get(i+1)) > 0) {
+          // Not sorted so fail the test
+          fail("ArrayList is not sorted, and it should be");
+        }
+      }
+    } finally {
+      cluster.shutdown();
+    }
+  }
+  
   @Test
   public void testDeletingBlocks() throws IOException {
     HdfsConfiguration conf = new HdfsConfiguration();