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From "Arun Suresh (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-7858) Improve HA Namenode Failover detection on the client
Date Fri, 24 Jul 2015 07:24:06 GMT

     [ https://issues.apache.org/jira/browse/HDFS-7858?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Arun Suresh updated HDFS-7858:
------------------------------
    Attachment: HDFS-7858.8.patch

Updating patch :

* Fixing whitespace issues
* bq. Now, if ALL proxies return FAILOVER_AND_RETRY, the operation is failed (since there
are no proxies to failover to)
Reverting this behavior. Since I think the assumption (atleast in many of the testcases) is
that FAILOVER_AND_RETRY implies just RETRY if no other proxy exists to failover to.


> 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
>              Labels: BB2015-05-TBR
>         Attachments: HDFS-7858.1.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-7858.8.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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