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https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13245729#comment-13245729
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Bikas Saha commented on HDFS-3077:
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Nice doc! Greatly sped up understanding the design instead of having to grok it
from the patch :)
I think it will help clarify the doc, if you add the explanation for Hari's
example. Even though epoch 2 is persisted on JN1, its last log segment is still
tied to epoch 1 and it needs to sync its last log segment with JN2/JN3. Are you
proposing that JN1 drop its last edits in progress and pick up the
corresponding finalized segment from JN1/JN2. Or is it TBD?
Btw, there is some new code here but there seems to be some code in existing NN
that changes the sequential journal sync to parallel (based on reading your doc
and not your patch). I am guessing there will be other significant changes
going forward. Are you planning on committing this to a branch or directly to
trunk?
> 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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