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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3077) Quorum-based protocol for reading and writing edit logs
Date Fri, 06 Jul 2012 03:51:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13407684#comment-13407684

Suresh Srinivas commented on HDFS-3077:

Todd, I have not had time to look into the comments or the patch. Will try to get this done
in next few days.

As I said earlier, keeping JournalProtocol without adding Quorum semantics allows writers
that have different policy. Perhaps the protocols should be different and may be JournalProtocol
from 3092 can remain as is. Again this is an early thought - will spend time on this in next
few days.

Quick comment:
bq. I disagree with this statement. The commit protocol is strongly intertwined with the way
in which the server has to behave. For example, the "new epoch" command needs to provide back
certain information about the current state of the journals and previous paxos-style 'accepted'
decisions. Trying to shoehorn it into a generic protocol doesn't make much sense to me.

What do you mean by "paxos-style". How does it relate to ZAB?
> 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, hdfs-3077.txt, hdfs-3077.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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