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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3077) Quorum-based protocol for reading and writing edit logs
Date Tue, 18 Sep 2012 22:23:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13458245#comment-13458245
] 

Suresh Srinivas commented on HDFS-3077:
---------------------------------------

bq. This code has been committed on the branch for about 2 months, and the relevant patch
was first on this JIRA on April 2nd. I think it's a bit late to consider this fundamental
of a re-structure now.
I have not had time to look at the code. But at least, based on my earlier comment, that JournalNode
and protocol independent of this code is still possible.

The example I was thinking was slightly different:
1. NN1 is active. NN2 is standby
<long pause>
2. NN2 detects loss of active and becomes active. It then establishes its epoch.
3. NN1 unpauses and continues to becomes primary by establishing new epoch before realizing
it is no longer active.

Is this possible?
                
> Quorum-based protocol for reading and writing edit logs
> -------------------------------------------------------
>
>                 Key: HDFS-3077
>                 URL: https://issues.apache.org/jira/browse/HDFS-3077
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: ha, name-node
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: QuorumJournalManager (HDFS-3077)
>
>         Attachments: hdfs-3077-partial.txt, hdfs-3077.txt, hdfs-3077.txt, hdfs-3077.txt,
hdfs-3077.txt, hdfs-3077.txt, hdfs-3077.txt, hdfs-3077.txt, qjournal-design.pdf, qjournal-design.pdf
>
>
> Currently, one of the weak points of the HA design is that it relies on shared storage
such as an NFS filer for the shared edit log. One alternative that has been proposed is to
depend on BookKeeper, a ZooKeeper subproject which provides a highly available replicated
edit log on commodity hardware. This JIRA is to implement another alternative, based on a
quorum commit protocol, integrated more tightly in HDFS and with the requirements driven only
by HDFS's needs rather than more generic use cases. More details to follow.

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