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Date: Thu, 2 Jun 2011 08:42:47 +0000 (UTC)
From: "HariSree (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-2017) A partial rollback cause the new
 changes done after upgrade to be visible after rollback
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    [ https://issues.apache.org/jira/browse/HDFS-2017?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13042650#comment-13042650 ] 

HariSree commented on HDFS-2017:
--------------------------------

>You mean to say here the upgrade failed but Namenode started functioning?

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 .. 

>How is this possible? The directory that is rolled back will be consistent with the directories that were not upgraded previously and hence are not rolled back.

The difference in the directories is due to the second normal restart . Here(the 2nd restart-normal) , during loadfsimage , the 1st dir ll be loaded and written to other dirs during savenamespace (chktime incremented) .. Now if new changes are made and  we rollback .. 
 After rollback , since only the 1st dir ll be rollbacked and others left behind (since they dont 've previous dirs) , the rollbacked 1st dir ll not contain the new changes , while the others ll contain Delta  .. now the 2nd dir ll be loaded since its chktime is higher than the 1st dir's chktime , and will be written to all other dirs .. So , due to this , Delta will be available after this rollback ..

> During rollback new changes are indeed lost.

Yes , thats normal .. 


> 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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