HDFS-15849. ExpiredHeartbeats metric should be of Type.COUNTER. Contributed by Qi Zhu.

(cherry picked from commit 9501c698f4789188f744f3a1fba7f1a9bb9b8aa4)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -4249,7 +4249,8 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
     return blockManager.getMissingReplOneBlocksCount();
   }
   
-  @Metric({"ExpiredHeartbeats", "Number of expired heartbeats"})
+  @Metric(value = {"ExpiredHeartbeats", "Number of expired heartbeats"},
+      type = Metric.Type.COUNTER)
   public int getExpiredHeartbeats() {
     return datanodeStatistics.getExpiredHeartbeats();
   }

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

@@ -17,7 +17,7 @@
 */
 package org.apache.hadoop.hdfs;
 
-import static org.apache.hadoop.test.MetricsAsserts.assertGauge;
+import static org.apache.hadoop.test.MetricsAsserts.assertCounter;
 import static org.apache.hadoop.test.MetricsAsserts.getMetrics;
 import static org.junit.Assert.assertEquals;
 
@@ -143,7 +143,7 @@ public class TestDatanodeReport {
       assertReports(1, DatanodeReportType.DEAD, client, datanodes, null);
 
       Thread.sleep(5000);
-      assertGauge("ExpiredHeartbeats", 1, getMetrics("FSNamesystem"));
+      assertCounter("ExpiredHeartbeats", 1, getMetrics("FSNamesystem"));
     } finally {
       cluster.shutdown();
     }