HA : An alternative approach to clients handling Namenode failover.
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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 are
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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