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From "Hanisha Koneru (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HDFS-4025) QJM: Sychronize past log segments to JNs that missed them
Date Sat, 27 Aug 2016 01:42:20 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4025?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15440421#comment-15440421
] 

Hanisha Koneru edited comment on HDFS-4025 at 8/27/16 1:41 AM:
---------------------------------------------------------------

The 000.patch would start a syncJournal thread in each JournalNode. This thread periodically
syncs the journal node by getting the edit log manifest from another randomly picked journal
node. If the other journal node has an edit log which is missing from the current journal
node, it is downloaded from the other journal node's http server. The in progress log segments
are not synced in this process.

Thank you [~jingzhao] for all the guidance.


was (Author: hanishakoneru):
This patch would start a syncJournal thread in each JournalNode. This thread periodically
syncs the journal node by getting the edit log manifest from another randomly picked journal
node. If the other journal node has an edit log which is missing from the current journal
node, it is downloaded from the other journal node's http server. The in progress log segments
are not synced in this process.

Thank you [~jingzhao] for all the guidance.

> 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)
>
>         Attachments: HDFS-4025.000.patch
>
>
> 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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