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https://issues.apache.org/jira/browse/HDFS-17368?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Xiaoqiao He resolved HDFS-17368.
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Fix Version/s: 3.5.0
Hadoop Flags: Reviewed
Resolution: Fixed
> HA: Standy should exit safemode when resources are from low available
> ---------------------------------------------------------------------
>
> Key: HDFS-17368
> URL: https://issues.apache.org/jira/browse/HDFS-17368
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Zilong Zhu
> Assignee: Zilong Zhu
> Priority: Major
> Labels: pull-request-available
> Fix For: 3.5.0
>
>
> The NameNodeResourceMonitor automatically enters safemode when it detects
> that the resources are not suffcient. NNRM is only in ANN. If both ANN and
> SNN enter SM due to low resources, and later SNN's disk space is restored,
> SNN willl become ANN and ANN will become SNN. However, at this point, SNN
> will not exit the SM, even if the disk is recovered.
> Consider the following scenario:
> * Initially, nn-1 is active and nn-2 is standby. The insufficient resources
> of both nn-1 and nn-2 in dfs.namenode.name.dir, the NameNodeResourceMonitor
> detects the resource issue and puts nn01 into safemode.
> * At this point, nn-1 is in safemode (ON) and active, while nn-2 is in
> safemode (OFF) and standby.
> * After a period of time, the resources in nn-2's dfs.namenode.name.dir
> recover, triggering failover.
> * Now, nn-1 is in safe mode (ON) and standby, while nn-2 is in safe mode
> (OFF) and active.
> * Afterward, the resources in nn-1's dfs.namenode.name.dir recover.
> * However, since nn-1 is standby but in safemode (ON), it unable to exit
> safe mode automatically.
> There are two possible ways fix this issues:
> # If SNN is detected to be in SM(because low resource), it will exit.
> # Or we already have HDFS-17231, we can revert HDFS-2914. Bringing NNRM back
> to SNN.
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