[jira] [Created] (HDFS-5399) Revisit SafeModeException and corresponding retry policies

["Jing Zhao (JIRA)" <ji...@apache.org>]

Jing Zhao created HDFS-5399:
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             Summary: Revisit SafeModeException and corresponding retry policies
                 Key: HDFS-5399
                 URL: https://issues.apache.org/jira/browse/HDFS-5399
             Project: Hadoop HDFS
          Issue Type: Improvement
    Affects Versions: 3.0.0
            Reporter: Jing Zhao
            Assignee: Jing Zhao


Currently for NN SafeMode, we have the following corresponding retry policies:

# In non-HA setup, the client will retry if the NN is in SafeMode. Specifically, the client side's RPC adopts MultipleLinearRandomRetry policy if a SafeModeException is wrapped in RemoteException.
# In HA setup, the client will retry if the NN is Active and in SafeMode. Specifically, the SafeModeException is wrapped as a RetriableException in the server side. Client side's RPC uses FailoverOnNetworkExceptionRetry policy which recognizes RetriableException (see HDFS-5291).

There are several issues in the current implementation:
# The NN SafeMode can be a "Manual" SafeMode (i.e., started by administrator through CLI), and the clients may not want to retry on this type of SafeMode.
# We should have a single generic strategy to address the mapping between SafeMode and retry policy for both HA and non-HA setup. A possible straightforward solution is to always wrap the SafeModeException in the RetriableException to indicate that the clients should retry.



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