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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2017) A partial rollback cause the new changes done after upgrade to be visible after rollback
Date Tue, 07 Jun 2011 00:18:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2017?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13045219#comment-13045219
] 

Suresh Srinivas commented on HDFS-2017:
---------------------------------------

> Here , it is the Namenode process stopping abnormally(due to external cause) just after
upgrade of the 1st name directory . After that , we're again starting it normally (REGULAR)
and it is starting up fine .. 

You started the namenode after failed upgrade? Generally what you do is, rollback when upgrade
fails. Ensure upgrade is successful before going ahead with the service.

However I do see a need for change. The system should not continue with its service when upgrade
fails. It should ensure user performs rollback.

> A partial rollback cause the new changes done after upgrade to be visible after rollback
> ----------------------------------------------------------------------------------------
>
>                 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
>            Priority: Minor
>              Labels: rollback, upgrade
>
> 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 ..
>  
> This is not the case with a SUCCESSFUL Upgrade/Rollback (New changes lost after rollback)..

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