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From "Sanjay Radia (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3077) Quorum-based protocol for reading and writing edit logs
Date Wed, 10 Oct 2012 23:19:52 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13473667#comment-13473667
] 

Sanjay Radia commented on HDFS-3077:
------------------------------------

{quote}
bq. Lets merge the newEpoch and prepareRecovery. Given that this works for ZAB I still fail
to see why it cannot work for us. I think because of (1), merging the two steps will no longer
be an issue.
I still don't understand why this is better and not just different. If you and Suresh want
to make the change, it's OK by me, but I expect that you will re-run the same validation before
committing (eg run the randomized fault test a few hundred thousand times). This testing found
a bunch of errors in the design before, so any chance to the design should go through the
same test regimen to make sure we aren't missing some subtlety.
{quote}

Okay, I assume that the tests are also in the branch. 
Have filed HDFS-4028 for this.


                
> 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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