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https://issues.apache.org/jira/browse/HDFS-7314?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14297133#comment-14297133
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Ming Ma commented on HDFS-7314:
-------------------------------
Thanks, [~jira.shegalov]. That is interesting. That might work when
applications request new FileSystem object. However, there is the scenario
where applications still hold the reference of aborted FileSystem object and
want to use that to create files; then applications need to be modified to
catch the exception and recreate the FileSystem object? At the beginning of the
jira, one of the 3 solutions proposed is to keep DistributedFileSystem alive
and recreate DFSClient. Regarding of the approach, it will be good to keep it
transparent to the applications.
> Aborted DFSClient's impact on long running service like YARN
> ------------------------------------------------------------
>
> Key: HDFS-7314
> URL: https://issues.apache.org/jira/browse/HDFS-7314
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Ming Ma
> Assignee: Ming Ma
> Attachments: HDFS-7314-2.patch, HDFS-7314-3.patch, HDFS-7314-4.patch,
> HDFS-7314-5.patch, HDFS-7314-6.patch, HDFS-7314-7.patch, HDFS-7314.patch
>
>
> It happened in YARN nodemanger scenario. But it could happen to any long
> running service that use cached instance of DistrbutedFileSystem.
> 1. Active NN is under heavy load. So it became unavailable for 10 minutes;
> any DFSClient request will get ConnectTimeoutException.
> 2. YARN nodemanager use DFSClient for certain write operation such as log
> aggregator or shared cache in YARN-1492. DFSClient used by YARN NM's
> renewLease RPC got ConnectTimeoutException.
> {noformat}
> 2014-10-29 01:36:19,559 WARN org.apache.hadoop.hdfs.LeaseRenewer: Failed to
> renew lease for [DFSClient_NONMAPREDUCE_-550838118_1] for 372 seconds.
> Aborting ...
> {noformat}
> 3. After DFSClient is in Aborted state, YARN NM can't use that cached
> instance of DistributedFileSystem.
> {noformat}
> 2014-10-29 20:26:23,991 INFO
> org.apache.hadoop.yarn.server.nodemanager.containermanager.localizer.ResourceLocalizationService:
> Failed to download rsrc...
> java.io.IOException: Filesystem closed
> at org.apache.hadoop.hdfs.DFSClient.checkOpen(DFSClient.java:727)
> at org.apache.hadoop.hdfs.DFSClient.getFileInfo(DFSClient.java:1780)
> at
> org.apache.hadoop.hdfs.DistributedFileSystem$17.doCall(DistributedFileSystem.java:1124)
> at
> org.apache.hadoop.hdfs.DistributedFileSystem$17.doCall(DistributedFileSystem.java:1120)
> at
> org.apache.hadoop.fs.FileSystemLinkResolver.resolve(FileSystemLinkResolver.java:81)
> at
> org.apache.hadoop.hdfs.DistributedFileSystem.getFileStatus(DistributedFileSystem.java:1120)
> at org.apache.hadoop.yarn.util.FSDownload.copy(FSDownload.java:237)
> at org.apache.hadoop.yarn.util.FSDownload.call(FSDownload.java:340)
> at org.apache.hadoop.yarn.util.FSDownload.call(FSDownload.java:57)
> at java.util.concurrent.FutureTask.run(FutureTask.java:262)
> at
> java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
> at java.util.concurrent.FutureTask.run(FutureTask.java:262)
> at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
> at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
> at java.lang.Thread.run(Thread.java:745)
> {noformat}
> We can make YARN or DFSClient more tolerant to temporary NN unavailability.
> Given the callstack is YARN -> DistributedFileSystem -> DFSClient, this can
> be addressed at different layers.
> * YARN closes the DistributedFileSystem object when it receives some well
> defined exception. Then the next HDFS call will create a new instance of
> DistributedFileSystem. We have to fix all the places in YARN. Plus other HDFS
> applications need to address this as well.
> * DistributedFileSystem detects Aborted DFSClient and create a new instance
> of DFSClient. We will need to fix all the places DistributedFileSystem calls
> DFSClient.
> * After DFSClient gets into Aborted state, it doesn't have to reject all
> requests , instead it can retry. If NN is available again it can transition
> to healthy state.
> Comments?
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