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https://issues.apache.org/jira/browse/HDFS-5889?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13897992#comment-13897992
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Tsz Wo (Nicholas), SZE commented on HDFS-5889:
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Thanks.  It actually cannot send NameNodeFile.IMAGE_UPGRADE file since it can 
only send NameNodeFile.IMAGE files.  Will also change it to support 
IMAGE_UPGRADE.

> When rolling upgrade is in progress, standby NN should create checkpoint for 
> downgrade.
> ---------------------------------------------------------------------------------------
>
>                 Key: HDFS-5889
>                 URL: https://issues.apache.org/jira/browse/HDFS-5889
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>            Reporter: Tsz Wo (Nicholas), SZE
>            Assignee: Tsz Wo (Nicholas), SZE
>         Attachments: h5889_20140211.patch
>
>
> After rolling upgrade is started and checkpoint is disabled, the edit log may 
> grow to a huge size.  It is not a problem if rolling upgrade is finalized 
> normally since NN keeps the current state in memory and it writes a new 
> checkpoint during finalize.  However, it is a problem if admin decides to 
> downgrade.  It could take a long time to apply edit log.  Rollback does not 
> have such problem.



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