commit dcb9796642320efb72df3817eba3625e778f23b4

Author: Hemanth Yamijala <yhemanth@yahoo-inc.com>
Date:   Fri Mar 19 13:26:36 2010 +0530

    MAPREDUCE:1417 from https://issues.apache.org/jira/secure/attachment/12439247/MAPREDUCE-1417-20.patch
    
    +++ b/YAHOO-CHANGES.txt
    +    MAPREDUCE-1417. Update forrest documentation for private
    +    and public distributed cache files. (Ravi Gummadi via yhemanth)
    +


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.20-security-patches@1077340 13f79535-47bb-0310-9956-ffa450edef68

src/docs/src/documentation/content/xdocs/mapred_tutorial.xml

@@ -1914,7 +1914,36 @@
           <code>mapred.job.classpath.{files|archives}</code>. Similarly the
           cached files that are symlinked into the working directory of the
           task can be used to distribute native libraries and load them.</p>
-          
+          <section>
+            <title>Private and Public DistributedCache Files</title>
+            <p>DistributedCache files can be private or public, that 
+               determines how they can be shared on the slave nodes.</p>
+            <ul>
+              <li>"Private" DistributedCache files are cached in a local
+              directory private to the user whose jobs need these
+              files. These files are shared by all
+              tasks and jobs of the specific user only and cannot be accessed by
+              jobs of other users on the slaves. A DistributedCache file becomes private by
+              virtue of its permissions on the file system where the files
+              are uploaded, typically HDFS. If the file has no world readable
+              access, or if the directory path leading to the file has no
+              world executable access for lookup, then the file becomes private.
+              </li>
+              <li>"Public" DistributedCache files are cached in a global
+              directory and the file access is setup such that they are 
+              publicly visible to all users. These files can be shared by
+              tasks and jobs of all users on the slaves.
+              A DistributedCache file becomes public by virtue of its permissions
+              on the file system where the files are uploaded, typically HDFS. 
+              If the file has world readable access, AND if the directory
+              path leading to the file has world executable access for lookup,
+              then the file becomes public. In other words, if the user intends
+              to make a file publicly available to all users, the file permissions
+              must be set to be world readable, and the directory permissions
+              on the path leading to the file must be world executable. 
+              </li>
+            </ul>
+          </section>
         </section>
         
         <section>