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https://issues.apache.org/jira/browse/HDFS-15555?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17840312#comment-17840312
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Takanobu Asanuma commented on HDFS-15555:
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[~chuanjie.duan] ConnectException is an instance of SocketException.
Therefore, the if statement can still catch a ConnectException.
> RBF: Refresh cacheNS when SocketException occurs
> ------------------------------------------------
>
> Key: HDFS-15555
> URL: https://issues.apache.org/jira/browse/HDFS-15555
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: rbf
> Affects Versions: 3.3.1, 3.4.0
> Environment: HDFS 3.3.0, Java 11
> Reporter: Akira Ajisaka
> Assignee: Akira Ajisaka
> Priority: Major
> Labels: pull-request-available
> Fix For: 3.3.1, 3.4.0
>
> Time Spent: 2.5h
> Remaining Estimate: 0h
>
> Problem:
> When active NameNode is restarted and loading fsimage, DFSRouters
> significantly slow down.
> Investigation:
> When active NameNode is restarted and loading fsimage, RouterRpcClient
> receives SocketException. Since
> RouterRpcClient#isUnavailableException(IOException) returns false when the
> argument is SocketException, the MembershipNameNodeResolver#cacheNS is not
> refreshed. That's why the order of the NameNodes returned by
> MemberShipNameNodeResolver#getNamenodesForNameserviceId(String) is unchanged
> and the active NameNode is still returned first. Therefore RouterRpcClient
> still tries to connect to the NameNode that is loading fsimage.
> After loading the fsimage, the NameNode throws StandbyException. The
> exception is one of the 'Unavailable Exception' and the cacheNS is refreshed.
> Workaround:
> Stop NameNode and wait 1 minute before starting NameNode instead of
> restarting.
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