HADOOP-5519. Remove claims from mapred-default.xml that prime numbers of tasks are helpful. (Owen O'Malley via szetszwo)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/core/branches/branch-0.20@756859 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -788,6 +788,9 @@ Release 0.20.0 - Unreleased
     HADOOP-5520. Fix a typo in disk quota help message.  (Ravi Phulari
     via szetszwo)
 
+    HADOOP-5519. Remove claims from mapred-default.xml that prime numbers
+    of tasks are helpful.  (Owen O'Malley via szetszwo)
+
 Release 0.19.2 - Unreleased
 
   BUG FIXES

src/mapred/mapred-default.xml

@@ -323,8 +323,7 @@
 <property>
   <name>mapred.map.tasks</name>
   <value>2</value>
-  <description>The default number of map tasks per job.  Typically set
-  to a prime several times greater than number of available hosts.
+  <description>The default number of map tasks per job.
   Ignored when mapred.job.tracker is "local".  
   </description>
 </property>
@@ -332,9 +331,10 @@
 <property>
   <name>mapred.reduce.tasks</name>
   <value>1</value>
-  <description>The default number of reduce tasks per job.  Typically set
-  to a prime close to the number of available hosts.  Ignored when
-  mapred.job.tracker is "local".
+  <description>The default number of reduce tasks per job. Typically set to 99%
+  of the cluster's reduce capacity, so that if a node fails the reduces can 
+  still be executed in a single wave.
+  Ignored when mapred.job.tracker is "local".
   </description>
 </property>