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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3092) Enable journal protocol based editlog streaming for standby namenode
Date Mon, 02 Apr 2012 18:25:26 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3092?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13244410#comment-13244410
] 

Todd Lipcon commented on HDFS-3092:
-----------------------------------

bq. This is what I was thinking - when roll is called from NN, it includes the version # from
journalList ZK node. It gets recorded in the start segment transaction in the editlog. Does
that work? Did I understand your comment correctly?

Yes, that solves the problem, but then requires that the recovery protocol open up and read
the edits out of the logs. It also leaks the edits storage mechanism into the edits contents,
so I don't think it's quite the right design.

The solution I'm using in HDFS-3077 is to keep an extra file in the edits directory which
includes the version number. During recovery, edits-in-progress on a logger whose version
number is out of date with respect to the others can be removed.

The thing is, once you've implemented all of this, I don't think your solution is any less
complex than the one in HDFS-3077 :)
                
> Enable journal protocol based editlog streaming for standby namenode
> --------------------------------------------------------------------
>
>                 Key: HDFS-3092
>                 URL: https://issues.apache.org/jira/browse/HDFS-3092
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: ha, name-node
>    Affects Versions: 0.24.0, 0.23.3
>            Reporter: Suresh Srinivas
>            Assignee: Suresh Srinivas
>         Attachments: MultipleSharedJournals.pdf
>
>
> Currently standby namenode relies on reading shared editlogs to stay current with the
active namenode, for namespace changes. BackupNode used streaming edits from active namenode
for doing the same. This jira is to explore using journal protocol based editlog streams for
the standby namenode. A daemon in standby will get the editlogs from the active and write
it to local edits. To begin with, the existing standby mechanism of reading from a file, will
continue to be used, instead of from shared edits, from the local edits.

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