HDFS-9484. NNThroughputBenchmark$BlockReportStats should not send empty block reports. Contributed by Mingliang Liu.

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

@@ -2436,6 +2436,9 @@ Release 2.8.0 - UNRELEASED
     HDFS-9429. Tests in TestDFSAdminWithHA intermittently fail with
     EOFException (Xiao Chen via Colin P. McCabe)
 
+    HDFS-9484. NNThroughputBenchmark$BlockReportStats should not send empty
+    block reports. (Mingliang Liu via shv)
+
 Release 2.7.3 - UNRELEASED
 
   INCOMPATIBLE CHANGES

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

@@ -925,7 +925,7 @@ public class NNThroughputBenchmark implements Tool {
     NamespaceInfo nsInfo;
     DatanodeRegistration dnRegistration;
     DatanodeStorage storage; //only one storage 
-    final ArrayList<BlockReportReplica> blocks;
+    final List<BlockReportReplica> blocks;
     int nrBlocks; // actual number of blocks
     BlockListAsLongs blockReportList;
     final int dnIdx;
@@ -938,7 +938,7 @@ public class NNThroughputBenchmark implements Tool {
 
     TinyDatanode(int dnIdx, int blockCapacity) throws IOException {
       this.dnIdx = dnIdx;
-      this.blocks = new ArrayList<BlockReportReplica>(blockCapacity);
+      this.blocks = Arrays.asList(new BlockReportReplica[blockCapacity]);
       this.nrBlocks = 0;
     }
 
@@ -1013,7 +1013,7 @@ public class NNThroughputBenchmark implements Tool {
         Block block = new Block(blocks.size() - idx, 0, 0);
         blocks.set(idx, new BlockReportReplica(block));
       }
-      blockReportList = BlockListAsLongs.EMPTY;
+      blockReportList = BlockListAsLongs.encode(blocks);
     }
 
     BlockListAsLongs getBlockReportList() {