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Date: Tue, 2 Oct 2012 10:41:12 +1100 (NCT)
From: "Todd Lipcon (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-3077) Quorum-based protocol for reading
 and writing edit logs
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    [ https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13467326#comment-13467326 ] 

Todd Lipcon commented on HDFS-3077:
-----------------------------------

BTW, regarding field debuggability, there are several decisions to help that:
1) The protobuf-serialized files (paxos accepted recovery files) include the protobuf in serialized binary form followed by the actual text content of them, so you can read them with a standard tool like "strings" or "less"
2) The epoch/promise files are text so you can read them with standard tools.

Combined with the log messages that are output on any new segment, you can match that against file ctimes easily as well.
                
> 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.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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