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From "Nicolas Liochon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4754) Add an API in the namenode to mark a datanode as stale
Date Thu, 23 May 2013 21:03:21 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4754?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13665669#comment-13665669
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Nicolas Liochon commented on HDFS-4754:
---------------------------------------

I forgot the apache license on the file I added, hence the release audit warning. Any other
point I need to fix? once accepted for trunk, I would like to put it in branch 2 as well.
                
> Add an API in the namenode to mark a datanode as stale
> ------------------------------------------------------
>
>                 Key: HDFS-4754
>                 URL: https://issues.apache.org/jira/browse/HDFS-4754
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client, namenode
>            Reporter: Nicolas Liochon
>            Assignee: Nicolas Liochon
>            Priority: Critical
>         Attachments: 4754.v1.patch
>
>
> There is a detection of the stale datanodes in HDFS since HDFS-3703, with a timeout,
defaulted to 30s.
> There are two reasons to add an API to mark a node as stale even if the timeout is not
yet reached:
>  1) ZooKeeper can detect that a client is dead at any moment. So, for HBase, we sometimes
start the recovery before a node is marked staled. (even with reasonable settings as: stale:
20s; HBase ZK timeout: 30s
>  2) Some third parties could detect that a node is dead before the timeout, hence saving
us the cost of retrying. An example or such hw is Arista, presented here by [~tsuna] http://tsunanet.net/~tsuna/fsf-hbase-meetup-april13.pdf,
and confirmed in HBASE-6290.
> As usual, even if the node is dead it can comeback before the 10 minutes limit. So I
would propose to set a timebound. The API would be
> namenode.markStale(String ipAddress, int port, long durationInMs);
> After durationInMs, the namenode would again rely only on its heartbeat to decide.
> Thoughts?
> If there is no objections, and if nobody in the hdfs dev team has the time to spend some
time on it, I will give it a try for branch 2 & 3.

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