HDFS-8862. BlockManager#excessReplicateMap should use a HashMap. (yliu)

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

@@ -820,6 +820,8 @@ Release 2.8.0 - UNRELEASED
     HDFS-8845. DiskChecker should not traverse the entire tree (Chang Li via
     Colin P. McCabe)
 
+    HDFS-8862. BlockManager#excessReplicateMap should use a HashMap. (yliu)
+
   BUG FIXES
 
     HDFS-7501. TransactionsSinceLastCheckpoint can be negative on SBNs.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java

@@ -33,7 +33,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Queue;
 import java.util.Set;
-import java.util.TreeMap;
 import java.util.TreeSet;
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.concurrent.atomic.AtomicLong;
@@ -204,7 +203,7 @@ public class BlockManager implements BlockStatsMXBean {
    * DataNode. We'll eventually remove these extras.
    */
   public final Map<String, LightWeightLinkedSet<Block>> excessReplicateMap =
-    new TreeMap<String, LightWeightLinkedSet<Block>>();
+    new HashMap<>();
 
   /**
    * Store set of Blocks that need to be replicated 1 or more times.