[jira] [Commented] (HDFS-13079) Provide a config to start namenode in safemode state upto a certain transaction id

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

    [ https://issues.apache.org/jira/browse/HDFS-13079?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16426786#comment-16426786 ] 

Shashikant Banerjee commented on HDFS-13079:
--------------------------------------------

Thanks [~msingh] fir proposing this Jira and starting work on this and [~vagarychen] for the review comments. Patch v2 addresses the review comments.

Please have a look.

> Provide a config to start namenode in safemode state upto a certain transaction id
> ----------------------------------------------------------------------------------
>
>                 Key: HDFS-13079
>                 URL: https://issues.apache.org/jira/browse/HDFS-13079
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>            Reporter: Mukul Kumar Singh
>            Assignee: Shashikant Banerjee
>            Priority: Major
>         Attachments: HDFS-13079.001.patch, HDFS-13079.002.patch
>
>
> In some cases it necessary to rollback the Namenode back to a certain transaction id. This is especially needed when the user issues a {{rm -Rf -skipTrash}} by mistake.
> Rolling back to a transaction id helps in taking a peek at the filesystem at a particular instant. This jira proposes to provide a configuration variable using which the namenode can be started upto a certain transaction id. The filesystem will be in a readonly safemode which cannot be overridden manually. It will only be overridden by removing the config value from the config file. Please also note that this will not cause any changes in the filesystem state, the filesystem will be in safemode state and no changes to the filesystem state will be allowed.
> Please note that in case a checkpoint has already happened and the requested transaction id has been subsumed in an FSImage, then the namenode will be started with the next nearest transaction id. Further FSImage files and edits will be ignored.
> If the checkpoint hasn't happen then the namenode will be started with the exact transaction id.



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