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https://issues.apache.org/jira/browse/HDFS-7858?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14901642#comment-14901642
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Tsz Wo Nicholas Sze commented on HDFS-7858:
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> ... then those clients might not get a response soon enough to try the other
> NN.
[~asuresh], do you recall how long have you seen for the client waiting? I
might hit a similar problem recently.
> 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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