From 00ee0585abce44690e9784b21a1fe31ce30e06e6 Mon Sep 17 00:00:00 2001
From: Matthew Foley <mattf@apache.org>
Date: Sun, 12 Feb 2012 07:47:35 +0000
Subject: [PATCH] HADOOP-8052. Hadoop Metrics2 should emit Float.MAX_VALUE
 (instead of Double.MAX_VALUE) to avoid making Ganglia's gmetad core.
 Contributed by Varun Kapoor.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1243207 13f79535-47bb-0310-9956-ffa450edef68
---
 hadoop-common-project/hadoop-common/CHANGES.txt  |  6 +++++-
 .../apache/hadoop/metrics2/util/SampleStat.java  | 16 ++++++++++++----
 .../hadoop/metrics2/util/TestSampleStat.java     |  8 ++++----
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/hadoop-common-project/hadoop-common/CHANGES.txt b/hadoop-common-project/hadoop-common/CHANGES.txt
index e0dbe146d0d..dc1dcda4015 100644
--- a/hadoop-common-project/hadoop-common/CHANGES.txt
+++ b/hadoop-common-project/hadoop-common/CHANGES.txt
@@ -176,7 +176,11 @@ Release 0.23.2 - UNRELEASED
 
     HADOOP-8051 HttpFS documentation it is not wired to the generated site (tucu)
 
-   HADOOP-8055. Hadoop tarball distribution lacks a core-site.xml (harsh)
+    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 mattf)
 
 Release 0.23.1 - 2012-02-08 
 
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/util/SampleStat.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/util/SampleStat.java
index f154269698a..589062a691c 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/util/SampleStat.java
+++ b/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) {
diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/util/TestSampleStat.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/util/TestSampleStat.java
index 36ca6bb1664..0fb0ad8ace9 100644
--- a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/util/TestSampleStat.java
+++ b/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);
   }
 
 }