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https://issues.apache.org/jira/browse/HDFS-17368?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17813232#comment-17813232
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ASF GitHub Bot commented on HDFS-17368:
---------------------------------------
zhuzilong2013 opened a new pull request, #6518:
URL: https://github.com/apache/hadoop/pull/6518
### Description of PR
Refer to HDFS-17368.
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.
If SNN is detected to be in SM(because low resource), it will exit.
### How was this patch tested?
Test in a production environment
### For code changes:
- [ ] Does the title or this PR starts with the corresponding JIRA issue id
(e.g. 'HADOOP-17799. Your PR title ...')?
- [ ] Object storage: have the integration tests been executed and the
endpoint declared according to the connector-specific documentation?
- [ ] If adding new dependencies to the code, are these dependencies
licensed in a way that is compatible for inclusion under [ASF
2.0](http://www.apache.org/legal/resolved.html#category-a)?
- [ ] If applicable, have you updated the `LICENSE`, `LICENSE-binary`,
`NOTICE-binary` files?
> 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
> Priority: Major
>
> 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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