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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4177) Handling read failures during recovery‏ - when HMaster calls Namenode recovery, recovery may be a failure leading to read failure while splitting logs
Date Fri, 24 Aug 2012 03:48:42 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4177?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13440919#comment-13440919
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ramkrishna.s.vasudevan commented on HBASE-4177:
-----------------------------------------------

@N
I too think the problem is still there.  But internally here also we have not started working
on this yet.  At that time we had discussions that HDFS side also we need some changes and
Stack has already raised the same in HDFS JIRA.  Surely you can take a stab at it N.
                
> Handling read failures during recovery‏ - when HMaster calls Namenode recovery, recovery
may be a failure leading to read failure while splitting logs
> ------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-4177
>                 URL: https://issues.apache.org/jira/browse/HBASE-4177
>             Project: HBase
>          Issue Type: Bug
>          Components: master
>            Reporter: ramkrishna.s.vasudevan
>            Assignee: ramkrishna.s.vasudevan
>            Priority: Critical
>
> As per the mailing thread with the heading
> 'Handling read failures during recovery‏' we found this problem.
> As part of split Logs the HMaster calls Namenode recovery.  The recovery is an asynchronous
process. 
> In HDFS
> =======
> Even though client is getting the updated block info from Namenode on first
> read failure, client is discarding the new info and using the old info only
> to retrieve the data from datanode. So, all the read
> retries are failing. [Method parameter reassignment - Not reflected in
> caller]. 
> In HBASE
> =======
> In HMaster code we tend to wait for  1sec.  But if the recovery had some failure then
split log may not happen and may lead to dataloss.
> So may be we need to decide upon the actual delay that needs to be introduced once Hmaster
calls NN recovery.

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