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From "Nathan Roberts (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3092) Enable journal protocol based editlog streaming for standby namenode
Date Wed, 09 May 2012 19:59:49 GMT

    [ 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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