HADOOP-8052. Hadoop Metrics2 should emit Float.MAX_VALUE (instead of Double.MAX_VALUE) to avoid making Ganglia's gmetad core. (Varun Kapoor via Matt) - Merging r1243207 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23.1@1244280 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -225,6 +225,10 @@ Release 0.23.1 - 2012-02-08
 
    HADOOP-8055. Hadoop tarball distribution lacks a core-site.xml (harsh)
 
+   HADOOP-8052. Hadoop Metrics2 should emit Float.MAX_VALUE 
+   (instead of Double.MAX_VALUE) to avoid making Ganglia's gmetad core.
+   (Varun Kapoor via Matt)
+
 Release 0.23.0 - 2011-11-01 
 
   INCOMPATIBLE CHANGES

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/util/SampleStat.java

@@ -143,8 +143,16 @@ public class SampleStat {
   @SuppressWarnings("PublicInnerClass")
   public static class MinMax {
 
-    private double min = Double.MAX_VALUE;
-    private double max = Double.MIN_VALUE;
+    // Float.MAX_VALUE is used rather than Double.MAX_VALUE, even though the
+    // min and max variables are of type double.
+    // Float.MAX_VALUE is big enough, and using Double.MAX_VALUE makes 
+    // Ganglia core due to buffer overflow.
+    // The same reasoning applies to the MIN_VALUE counterparts.
+    static final double DEFAULT_MIN_VALUE = Float.MAX_VALUE;
+    static final double DEFAULT_MAX_VALUE = Float.MIN_VALUE;
+
+    private double min = DEFAULT_MIN_VALUE;
+    private double max = DEFAULT_MAX_VALUE;
 
     public void add(double value) {
       if (value > max) max = value;
@@ -155,8 +163,8 @@ public class SampleStat {
     public double max() { return max; }
 
     public void reset() {
-      min = Double.MAX_VALUE;
-      max = Double.MIN_VALUE;
+      min = DEFAULT_MIN_VALUE;
+      max = DEFAULT_MAX_VALUE;
     }
 
     public void reset(MinMax other) {

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/util/TestSampleStat.java

@@ -36,8 +36,8 @@ public class TestSampleStat {
     assertEquals("mean", 0.0, stat.mean(), EPSILON);
     assertEquals("variance", 0.0, stat.variance(), EPSILON);
     assertEquals("stddev", 0.0, stat.stddev(), EPSILON);
-    assertEquals("min", Double.MAX_VALUE, stat.min(), EPSILON);
-    assertEquals("max", Double.MIN_VALUE, stat.max(), EPSILON);
+    assertEquals("min", SampleStat.MinMax.DEFAULT_MIN_VALUE, stat.min(), EPSILON);
+    assertEquals("max", SampleStat.MinMax.DEFAULT_MAX_VALUE, stat.max(), EPSILON);
 
     stat.add(3);
     assertEquals("num samples", 1L, stat.numSamples());
@@ -60,8 +60,8 @@ public class TestSampleStat {
     assertEquals("mean", 0.0, stat.mean(), EPSILON);
     assertEquals("variance", 0.0, stat.variance(), EPSILON);
     assertEquals("stddev", 0.0, stat.stddev(), EPSILON);
-    assertEquals("min", Double.MAX_VALUE, stat.min(), EPSILON);
-    assertEquals("max", Double.MIN_VALUE, stat.max(), EPSILON);
+    assertEquals("min", SampleStat.MinMax.DEFAULT_MIN_VALUE, stat.min(), EPSILON);
+    assertEquals("max", SampleStat.MinMax.DEFAULT_MAX_VALUE, stat.max(), EPSILON);
   }
 
 }