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Date: Wed, 4 Apr 2012 15:49:24 +0000 (UTC)
From: "Flavio Junqueira (Commented) (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=13246385#comment-13246385 ] 

Flavio Junqueira commented on HDFS-3092:
----------------------------------------

bq. Is there a way to turn off the striping even if Quorom size (Q) is less than Ensemble size (E)?
We like the idea that each Journal file contains ALL entries.
Our default config: Q is 2 and set of JDs is 3 (roughly equivalent to E).

Right now the write set is the same as the ack set, since we haven't had the use case you suggest so far. We have anticipated the need of different ways of scheduling reads and writes, and it is fairly simple to make it cover your use case. Ivan had actually suggested this separation between ack sets and write sets previously to deal with slow disks. 

I have tried to reflect this discussion in BOOKKEEPER-208 if you're interested.  
                
> 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, 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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