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https://issues.apache.org/jira/browse/HDFS-4025?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13475551#comment-13475551
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liang xie commented on HDFS-4025:
---------------------------------

Hi Todd, are you working on this? I'm interested in doing so, if not.
                
> QJM: Sychronize past log segments to JNs that missed them
> ---------------------------------------------------------
>
>                 Key: HDFS-4025
>                 URL: https://issues.apache.org/jira/browse/HDFS-4025
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: ha
>    Affects Versions: QuorumJournalManager (HDFS-3077)
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: QuorumJournalManager (HDFS-3077)
>
>
> Currently, if a JournalManager crashes and misses some segment of logs, and 
> then comes back, it will be re-added as a valid part of the quorum on the 
> next log roll. However, it will not have a complete history of log segments 
> (i.e any individual JN may have gaps in its transaction history). This 
> mirrors the behavior of the NameNode when there are multiple local 
> directories specified.
> However, it would be better if a background thread noticed these gaps and 
> "filled them in" by grabbing the segments from other JournalNodes. This 
> increases the resilience of the system when JournalNodes get reformatted or 
> otherwise lose their local disk.

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