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From "liang xie (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4025) QJM: Sychronize past log segments to JNs that missed them
Date Sat, 13 Oct 2012 08:23:03 GMT

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

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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