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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 Mon, 01 Oct 2012 18:19:11 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13467041#comment-13467041
] 

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

Section 2.9
The use of the term "master" can be confused with  "recovery coordinator". The master JN is
the source for the journal synchronization. The section title uses the word "recovery" - this
word is also used section 2.8.
* clarify this in the section 
* the journal can be sync'ed from multiple sources - shouldn't this be a list of "Master(s)"?
* use another term: "journal-sync-master(s)" or "journal-sycn-source(s)" - I prefer the word
"source"
* Change title of the section to be "Journal Synchronization - Choosing the Source" (or Master?).

Q. is Synchronization needed before proceeding when you have a Quorum of JNs that have all
the transaction. That is, in that case does the "acceptRecovery" operation (section 2.8) force
the last log segment in each of the JNs to be consistently finalized? Either, way please clarify
this in section 2.9. (Clearly all unsync'ed JNs have to sync with one of the other JNs.) I
think you are using the design and code of HDFS-3092 but at times I am not sure when i read
this section.

                
> 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.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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