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https://issues.apache.org/jira/browse/HDFS-14655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16923663#comment-16923663
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Chen Liang commented on HDFS-14655:
-----------------------------------

[~xkrogen] I agree. But in the particular case here, the only concern I think, 
is if one thread stuck talking to a (potentially dead) JN in a previous call, 
having another thread talking to this JN will likely stuck as well. In which 
case parallelism does not give much benefit, but just overhead. But if it is 
for some other reason one thread is slow, having more threads helps. I don't 
have a strong opinion on single thread vs no more than some number of threads 
here. Either way is fine by me.

> [SBN Read] Namenode crashes if one of The JN is down
> ----------------------------------------------------
>
>                 Key: HDFS-14655
>                 URL: https://issues.apache.org/jira/browse/HDFS-14655
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Harshakiran Reddy
>            Assignee: Ayush Saxena
>            Priority: Major
>         Attachments: HDFS-14655-01.patch, HDFS-14655.poc.patch
>
>
> {noformat}
> 2019-07-04 17:35:54,064 | INFO  | Logger channel (from parallel executor) to 
> XXXXXXX/XXXXXXX | Retrying connect to server: XXXXXXX/XXXXXXX. Already tried 
> 9 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, 
> sleepTime=1000 MILLISECONDS) | Client.java:975
> 2019-07-04 17:35:54,087 | FATAL | Edit log tailer | Unknown error encountered 
> while tailing edits. Shutting down standby NN. | EditLogTailer.java:474
> java.lang.OutOfMemoryError: unable to create new native thread
>       at java.lang.Thread.start0(Native Method)
>       at java.lang.Thread.start(Thread.java:717)
>       at 
> java.util.concurrent.ThreadPoolExecutor.addWorker(ThreadPoolExecutor.java:957)
>       at 
> java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1378)
>       at 
> com.google.common.util.concurrent.MoreExecutors$ListeningDecorator.execute(MoreExecutors.java:440)
>       at 
> com.google.common.util.concurrent.AbstractListeningExecutorService.submit(AbstractListeningExecutorService.java:56)
>       at 
> org.apache.hadoop.hdfs.qjournal.client.IPCLoggerChannel.getJournaledEdits(IPCLoggerChannel.java:565)
>       at 
> org.apache.hadoop.hdfs.qjournal.client.AsyncLoggerSet.getJournaledEdits(AsyncLoggerSet.java:272)
>       at 
> org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager.selectRpcInputStreams(QuorumJournalManager.java:533)
>       at 
> org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager.selectInputStreams(QuorumJournalManager.java:508)
>       at 
> org.apache.hadoop.hdfs.server.namenode.JournalSet.selectInputStreams(JournalSet.java:275)
>       at 
> org.apache.hadoop.hdfs.server.namenode.FSEditLog.selectInputStreams(FSEditLog.java:1681)
>       at 
> org.apache.hadoop.hdfs.server.namenode.FSEditLog.selectInputStreams(FSEditLog.java:1714)
>       at 
> org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer.doTailEdits(EditLogTailer.java:307)
>       at 
> org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer$EditLogTailerThread.doWork(EditLogTailer.java:460)
>       at 
> org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer$EditLogTailerThread.access$300(EditLogTailer.java:410)
>       at 
> org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer$EditLogTailerThread$1.run(EditLogTailer.java:427)
>       at java.security.AccessController.doPrivileged(Native Method)
>       at javax.security.auth.Subject.doAs(Subject.java:360)
>       at 
> org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1709)
>       at 
> org.apache.hadoop.security.SecurityUtil.doAsLoginUserOrFatal(SecurityUtil.java:483)
>       at 
> org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer$EditLogTailerThread.run(EditLogTailer.java:423)
> 2019-07-04 17:35:54,112 | INFO  | Edit log tailer | Exiting with status 1: 
> java.lang.OutOfMemoryError: unable to create new native thread | 
> ExitUtil.java:210
> {noformat}



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