[GitHub] [hadoop] slfan1989 commented on a diff in pull request #4606: HDFS-16678. RBF should supports disable getNodeUsage() in RBFMetrics

[GitBox <gi...@apache.org>]

slfan1989 commented on code in PR #4606:
URL: https://github.com/apache/hadoop/pull/4606#discussion_r931795987


##########
hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/metrics/RBFMetrics.java:
##########
@@ -537,35 +547,34 @@ public int getNumEnteringMaintenanceDataNodes() {
 
   @Override // NameNodeMXBean
   public String getNodeUsage() {
-    float median = 0;
-    float max = 0;
-    float min = 0;
-    float dev = 0;
+    double median = 0;
+    double max = 0;
+    double min = 0;
+    double dev = 0;
 
     final Map<String, Map<String, Object>> info = new HashMap<>();
     try {
-      RouterRpcServer rpcServer = this.router.getRpcServer();
-      DatanodeInfo[] live = rpcServer.getDatanodeReport(
-          DatanodeReportType.LIVE, false, timeOut);
+      DatanodeInfo[] live = null;
+      if (this.enableGetDNUsage) {
+        RouterRpcServer rpcServer = this.router.getRpcServer();
+        live = rpcServer.getDatanodeReport(DatanodeReportType.LIVE, false, timeOut);
+      } else {
+        LOG.debug("Getting node usage is disabled.");
+      }
 
-      if (live.length > 0) {
-        float totalDfsUsed = 0;
-        float[] usages = new float[live.length];
+      if (live != null && live.length > 0) {
+        double[] usages = new double[live.length];
         int i = 0;
         for (DatanodeInfo dn : live) {
           usages[i++] = dn.getDfsUsedPercent();
-          totalDfsUsed += dn.getDfsUsedPercent();
         }
-        totalDfsUsed /= live.length;
         Arrays.sort(usages);
         median = usages[usages.length / 2];
         max = usages[usages.length - 1];
         min = usages[0];
 
-        for (i = 0; i < usages.length; i++) {
-          dev += (usages[i] - totalDfsUsed) * (usages[i] - totalDfsUsed);
-        }
-        dev = (float) Math.sqrt(dev / usages.length);
+        StandardDeviation deviation = new StandardDeviation();
+        dev = deviation.evaluate(usages);
       }
     } catch (IOException e) {
       LOG.error("Cannot get the live nodes: {}", e.getMessage());

Review Comment:
   I feel it would be better this way.
   
   ```
   LOG.error("Cannot get the live nodes.", e).
   ```



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