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https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13470680#comment-13470680
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Suresh Srinivas commented on HDFS-3077:
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bq. I'm not interested in changing the design substantially at this point
without a good reason. I've put several weeks into testing this design...
Todd, several people have put in a bunch of time in this as well, not just in
this jira, but also related HA jiras and HDFS-3092 which this jira
incorporates.
Just reviewing this design has required catching up with subtleties of Paxos
and ZAB. So the comments made here are not frivolous, but come with quite a bit
of investment of time. The design started saying it is ZAB like, then added
paxos and since then has gone back and forth. The interest in getting this
right is to ensure a critical component of HDFS is right.
The reason to do this is to make sure not only the design is correct, but is
simple and completely documented. This is more important given the complexity
of this solution and the need for other HDFS contributors to understand so it
can be maintained. This has been brought up Konstantin also in the mailing list.
I know you have spent a lot of time on this. I am okay if you do not want to
make further changes. But I think some of the changes that Sanjay is proposing
is worth considering, if it simplifies the design. In general, a reviewer's
feedback for a jira is not just to show design bugs, but also to provide
feedback on other things, such as maintainability, simplicity etc.
If you do not have cycles, it is understandable. Someone else can pick up the
work that comes out of these discussions.
> 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-test-merge.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,
> qjournal-design.pdf, qjournal-design.pdf, qjournal-design.pdf,
> qjournal-design.pdf, qjournal-design.tex, qjournal-design.tex
>
>
> 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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