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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 Tue, 09 Oct 2012 17:34:03 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13472575#comment-13472575
] 

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

I propose we do the following
# Recover all transactions. We do this in the same fashion as ZAB rather then the way you
suggested "the NN can run the recovery process for each of these earlier segments individually".
Note this requires two changes:
** The protocol message contents change - the response to phase 1 is highest txid and not
highest segment's txid. The JN recovers all previous  transactions from another JN.
** When a JN joins an existing writer it first syncs previous segments.
# 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 am fine doing this in 2 separate jiras after the merge if you prefer. You have already volunteered
to work on (1). Suresh or I can work on (2).

                
> 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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