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https://issues.apache.org/jira/browse/HDFS-5399?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13886208#comment-13886208
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Arpit Gupta commented on HDFS-5399:
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bq. The test you observed this issue in didn't run long enough for the standby
NN to leave startup safemode on its own before the failover was attempted. The
NN will delay processing block reports for block IDs it doesn't recognize
(because they're created in edits that the NN hasn't read yet) and then only on
transition to active do we fully catch up by reading all the edits, and then
re-process the delayed block reports, triggering the NN to leave startup
safemode.
Its not the test that directly fails. We see exceptions in the RM when its
trying to talk to HDFS or in RS when its trying to talk to HDFS which causes
the actual MR job etc to fail. So its not something that the test can control.
For example we are running an MR job and are periodically killing the active NN
and the job eventually fails as the tasks that want to talk to hdfs fail or the
RM runs into this exception causing the application to fail. Hence i would
argue that its a flaw in the test :).
> 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, for certain API call ("create"), the client will retry if
> the NN is in SafeMode. Specifically, the client side's RPC adopts
> MultipleLinearRandomRetry policy for a wrapped SafeModeException when retry
> is enabled.
> # 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 possible 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.
> # Client may want to retry on other API calls in non-HA setup.
> # 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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