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https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13245702#comment-13245702
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Suresh Srinivas commented on HDFS-3077:
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bq. I prefer JournalNode because every other daemon we have is a *Node. If
you're running it inside another process, I think we would just call it a
"JournalService" – or an "embedded JournalNode". I think of a daemon as a
standalone process.
I think that is fine. I have initial JournalService that is implemented as a
part of 3092. We will consolidate from your patch, this part of the code in
HDFS-3178.
bq. OK. This part I have done in the patch attached here and works pretty well,
so far. If you want, I'm happy to separate out the quorum completion code to
commit it ASAP so we can share code here.
This sounds good.
bq. I think the "standalone" nature of the approach outweighs what benefit we
might get by reusing ZK.
We can look into this in more detail. However, we will add a method called
fence() in the JournalProtocol, with epoch number.
I will get back to you on the last comment.
> 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
> Attachments: hdfs-3077-partial.txt, 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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