HDFS-11047. Remove deep copies of FinalizedReplica to alleviate heap consumption on DataNode. Contributed by Xiaobing Zhou

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

@@ -596,14 +596,13 @@ public class DirectoryScanner implements Runnable {
         diffs.put(bpid, diffRecord);
         
         statsRecord.totalBlocks = blockpoolReport.length;
-        List<FinalizedReplica> bl = dataset.getFinalizedBlocks(bpid);
-        FinalizedReplica[] memReport = bl.toArray(new FinalizedReplica[bl.size()]);
-        Arrays.sort(memReport); // Sort based on blockId
-  
+        final List<FinalizedReplica> bl = dataset.getFinalizedBlocks(bpid);
+        Collections.sort(bl); // Sort based on blockId
+
         int d = 0; // index for blockpoolReport
         int m = 0; // index for memReprot
-        while (m < memReport.length && d < blockpoolReport.length) {
-          FinalizedReplica memBlock = memReport[m];
+        while (m < bl.size() && d < blockpoolReport.length) {
+          FinalizedReplica memBlock = bl.get(m);
           ScanInfo info = blockpoolReport[d];
           if (info.getBlockId() < memBlock.getBlockId()) {
             if (!dataset.isDeletingBlock(bpid, info.getBlockId())) {
@@ -650,8 +649,8 @@ public class DirectoryScanner implements Runnable {
             ++m;
           }
         }
-        while (m < memReport.length) {
-          FinalizedReplica current = memReport[m++];
+        while (m < bl.size()) {
+          FinalizedReplica current = bl.get(m++);
           addDifference(diffRecord, statsRecord,
                         current.getBlockId(), current.getVolume());
         }

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

@@ -230,7 +230,16 @@ public interface FsDatasetSpi<V extends FsVolumeSpi> extends FSDatasetMBean {
    */
   VolumeFailureSummary getVolumeFailureSummary();
 
-  /** @return a list of finalized blocks for the given block pool. */
+  /**
+   * Gets a list of references to the finalized blocks for the given block pool.
+   * <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.
+   */
   List<FinalizedReplica> getFinalizedBlocks(String bpid);
 
   /** @return a list of finalized blocks for the given block pool. */

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

@@ -1842,16 +1842,23 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
   }
 
   /**
-   * Get the list of finalized blocks from in-memory blockmap for a block pool.
+   * Gets a list of references to the finalized blocks for the given block pool.
+   * <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.
    */
   @Override
   public List<FinalizedReplica> getFinalizedBlocks(String bpid) {
     try(AutoCloseableLock lock = datasetLock.acquire()) {
-      ArrayList<FinalizedReplica> finalized =
+      final ArrayList<FinalizedReplica> finalized =
           new ArrayList<FinalizedReplica>(volumeMap.size(bpid));
       for (ReplicaInfo b : volumeMap.replicas(bpid)) {
         if (b.getState() == ReplicaState.FINALIZED) {
-          finalized.add(new FinalizedReplica((FinalizedReplica) b));
+          finalized.add((FinalizedReplica)b);
         }
       }
       return finalized;