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From "HariSree (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-2017) A partial rollback cause the new changes done after upgrade to be visible after rollback
Date Tue, 31 May 2011 10:23:47 GMT
A partial rollback cause the new changes done after upgrade to be visible after rollback
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                 Key: HDFS-2017
                 URL: https://issues.apache.org/jira/browse/HDFS-2017
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: name-node
    Affects Versions: 0.20.1
            Reporter: HariSree


This is the scenario :

Namenode has 3 name dirs configured ..
1) Namenode upgrade starts - Upgrade fails after 1st directory is upgraded (2nd and 3rd dir
is left unchanged ..) { like , Namenode process down }
2) Namenode starts and new files written .. 
3) Namenode shutdown and rollbacked

Since Namenode is saving the latest image dir(the upgraded 1st dir since checkpointtime is
incremented during upgrade for this dir) will be loaded and saved to all dirs during loadfsimage
..

But if a ROLLBACK is done , the 1st dir will be rolled back (the older copy becomes current
and its checkpointtime is now LESS than other dirs ..) and others left behind since they dont
contain previous .. Now during loadfsimage , the 2nd dir will be selected since it has the
highest checkpoint time and saved to all dirs (including 1st ) .. Now due to this , the new
changes b/w UPGRADE and ROLLBACK present in 2nd dir gets reflected even after ROLLBACK ..
 
Now if we try to do a rollback again , all the previous states will be lost and delta becomes
permanent to all dirs .. and no way to go back to the PREVIOUS STATE 

This is not the case with a SUCCESSFUL Upgrade/Rollback (New changes lost after rollback)..


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