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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7858) Improve HA Namenode Failover detection on the client
Date Thu, 24 Sep 2015 14:08:04 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7858?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14906384#comment-14906384
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Tsz Wo Nicholas Sze commented on HDFS-7858:
-------------------------------------------

Never mind.  Thanks for the response.

> Improve HA Namenode Failover detection on the client
> ----------------------------------------------------
>
>                 Key: HDFS-7858
>                 URL: https://issues.apache.org/jira/browse/HDFS-7858
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client
>            Reporter: Arun Suresh
>            Assignee: Arun Suresh
>              Labels: BB2015-05-TBR
>             Fix For: 2.8.0
>
>         Attachments: HDFS-7858.1.patch, HDFS-7858.10.patch, HDFS-7858.10.patch, HDFS-7858.11.patch,
HDFS-7858.12.patch, HDFS-7858.13.patch, HDFS-7858.2.patch, HDFS-7858.2.patch, HDFS-7858.3.patch,
HDFS-7858.4.patch, HDFS-7858.5.patch, HDFS-7858.6.patch, HDFS-7858.7.patch, HDFS-7858.8.patch,
HDFS-7858.9.patch
>
>
> In an HA deployment, Clients are configured with the hostnames of both the Active and
Standby Namenodes.Clients will first try one of the NNs (non-deterministically) and if its
a standby NN, then it will respond to the client to retry the request on the other Namenode.
> If the client happens to talks to the Standby first, and the standby is undergoing some
GC / is busy, then those clients might not get a response soon enough to try the other NN.
> Proposed Approach to solve this :
> 1) Use hedged RPCs to simultaneously call multiple configured NNs to decide which is
the active Namenode.
> 2) Subsequent calls, will invoke the previously successful NN.
> 3) On failover of the currently active NN, the remaining NNs will be invoked to decide
which is the new active 



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