[jira] [Commented] (MAPREDUCE-4549) Distributed cache conflicts breaks backwards compatability

["Hudson (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4549?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13435029#comment-13435029 ] 

Hudson commented on MAPREDUCE-4549:
-----------------------------------

Integrated in Hadoop-Hdfs-0.23-Build #344 (See [https://builds.apache.org/job/Hadoop-Hdfs-0.23-Build/344/])
    svn merge -c -1369197 Reverting: MAPREDUCE-4503 in branch-0.23 until MAPREDUCE-4549 can be addressed. (Revision 1372573)

     Result = SUCCESS
bobby : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1372573
Files : 
* /hadoop/common/branches/branch-0.23/hadoop-mapreduce-project/CHANGES.txt
* /hadoop/common/branches/branch-0.23/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/util/MRApps.java
* /hadoop/common/branches/branch-0.23/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/test/java/org/apache/hadoop/mapreduce/v2/util/TestMRApps.java

                
> Distributed cache conflicts breaks backwards compatability
> ----------------------------------------------------------
>
>                 Key: MAPREDUCE-4549
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4549
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mrv2
>    Affects Versions: 0.23.3, 2.1.0-alpha, 3.0.0, 2.2.0-alpha
>            Reporter: Robert Joseph Evans
>            Assignee: Robert Joseph Evans
>            Priority: Critical
>
> I recently put in MAPREDUCE-4503 which went a bit too far, and broke backwards compatibility with 1.0 in distribtued cache entries.  This is to change the behavior of the distributed cache to more closely match that of 1.0.
> In 1.0 when adding in a cache archive link the first link would win (be the one that was created), not the last one as is the current behavior, when there were conflicts then all of the others were ignored and just did not get a symlink created, and finally no symlink was created for archives that had did not have a fragment in the URL.  
> To simulate this behavior after we parse the cache files and cache archives configuration we should walk through all conflicting links and pick the first link that has a fragment to win.  If no link has a fragment then it is just the first link wins.  All other conflicting links will have a warning an the name of the link will be changed to include a UUID.  If the same file is both in the distributed cache as a cache file and a cache archive we will throw an exception, for backwards compatibility.

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