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From "Arun Suresh (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7858) Improve HA Namenode Failover detection on the client
Date Tue, 31 Mar 2015 16:03:54 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7858?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14388750#comment-14388750
] 

Arun Suresh commented on HDFS-7858:
-----------------------------------

Thanks for the review [~jingzhao].

bq. I'm thinking that how about providing RequestHedgingInvocationHandler as a replacement
of RetryInvocationHandler? We need to add the retry logic into RequestHedgingInvocationHandler
but the whole layer may look more clean.

Yup.. that makes sense.. let me give a shot at refactoring.. and will post an updated patch
shortly

> 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
>            Reporter: Arun Suresh
>            Assignee: Arun Suresh
>         Attachments: HDFS-7858.1.patch, HDFS-7858.2.patch, HDFS-7858.2.patch, HDFS-7858.3.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) Since Zookeeper is already used as the failover controller, the clients could talk
to ZK and find out which is the active namenode before contacting it.
> 2) Long-lived DFSClients would have a ZK watch configured which fires when there is a
failover so they do not have to query ZK everytime to find out the active NN
> 2) Clients can also cache the last active NN in the user's home directory (~/.lastNN)
so that short-lived clients can try that Namenode first before querying ZK



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