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Date: Wed, 9 May 2012 19:59:49 +0000 (UTC)
From: "Nathan Roberts (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-3092) Enable journal protocol based
 editlog streaming for standby namenode
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    [ https://issues.apache.org/jira/browse/HDFS-3092?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13271737#comment-13271737 ] 

Nathan Roberts commented on HDFS-3092:
--------------------------------------

Eli, thanks for the writeup. 

One question on this statement "(ie option 1 is fundamentally slower)." We already double-buffer the editstreams in the namenode so isn't it true that users will only see latency effects if the buffering isn't able to keep up? In other words, isn't it the case that as long as the slowest journal is keeping up with demand, there's no significant difference in performance? 
                
> 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: ComparisonofApproachesforHAJournals.pdf, JNStates.png, MultipleSharedJournals.pdf, MultipleSharedJournals.pdf, MultipleSharedJournals.pdf, Removingfilerdependency.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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