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https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13458245#comment-13458245
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Suresh Srinivas commented on HDFS-3077:
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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before realizing it is no longer active.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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