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From "Uma Maheswara Rao G (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-2713) HA : An alternative approach to clients handling Namenode failover.
Date Wed, 21 Dec 2011 15:29:30 GMT
HA : An alternative approach to clients handling  Namenode failover.

                 Key: HDFS-2713
                 URL: https://issues.apache.org/jira/browse/HDFS-2713
             Project: Hadoop HDFS
          Issue Type: Sub-task
          Components: ha, hdfs client
    Affects Versions: HA branch (HDFS-1623)
            Reporter: Uma Maheswara Rao G
            Assignee: Uma Maheswara Rao G

This is the approach for client failover which we adopted when we developed HA for Hadoop.
I would like to propose thia approach for others to review & include in the HA implementation,
if found useful.

This is similar to the ConfiguredProxyProvider in the sense that the it takes the address
of both the Namenodes as the input. The major differences I can see from the current implementation
1) During failover, user threads can be controlled very accurately about *the time they wait
for active namenode* to be available, awaiting the retry. Beyond this, the threads will not
be made to wait; DFS Client will throw an Exception indicating that the operation has failed.
2) Failover happens in a seperate thread, not in the client application threads. The thread
will keep trying to find the Active Namenode until it succeeds. 
3) This also means that irrespective of whether the operation's RetryAction is RETRY_FAILOVER
or FAIL, the user thread can trigger the client's failover. 

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