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From "Suresh Srinivas (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3212) Persist the epoch received by the JournalService
Date Fri, 06 Apr 2012 00:16:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3212?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13247880#comment-13247880
] 

Suresh Srinivas commented on HDFS-3212:
---------------------------------------

bq. I don't think it's reasonable to put the epoch number inside the START transaction, because
that leaks the idea of epochs out of the journal manager layer into the NN layer.
I do not understand what you mean by NN layer. Epoch is a notion from JournalManager to the
JournalNode. Both need to understand this and provide appropriate guarantees.

bq. Also, if the JN restarts, when it comes up, how do you make sure that an old NN doesn't
come back to life with a startLogSegment transaction?
Can you give me an example. I am not sure I understand the issue.
                
> Persist the epoch received by the JournalService
> ------------------------------------------------
>
>                 Key: HDFS-3212
>                 URL: https://issues.apache.org/jira/browse/HDFS-3212
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: ha, name-node
>    Affects Versions: Shared journals (HDFS-3092)
>            Reporter: Suresh Srinivas
>
> epoch received over JournalProtocol should be persisted by JournalService.

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