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https://issues.apache.org/jira/browse/FLINK-4660?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15515997#comment-15515997
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Stephan Ewen commented on FLINK-4660:
-------------------------------------
It should have been fixed as of 2 days ago:
https://github.com/apache/flink/commit/3b8fe95ec728d59e3ffba2901450c56d7cca2b24
> HadoopFileSystem (with S3A) may leak connections, which cause job to stuck in
> a restarting loop
> -----------------------------------------------------------------------------------------------
>
> Key: FLINK-4660
> URL: https://issues.apache.org/jira/browse/FLINK-4660
> Project: Flink
> Issue Type: Bug
> Components: State Backends, Checkpointing
> Reporter: Zhenzhong Xu
> Priority: Critical
> Attachments: Screen Shot 2016-09-20 at 2.49.14 PM.png, Screen Shot
> 2016-09-20 at 2.49.32 PM.png
>
>
> Flink job with checkpoints enabled and configured to use S3A file system
> backend, sometimes experiences checkpointing failure due to S3 consistency
> issue. This behavior is also reported by other people and documented in
> https://issues.apache.org/jira/browse/FLINK-4218.
> This problem gets magnified by current HadoopFileSystem implementation, which
> can potentially leak S3 client connections, and eventually get into a
> restarting loop with “Timeout waiting for a connection from pool” exception
> thrown from aws client.
> I looked at the code, seems HadoopFileSystem.java never invoke close() method
> on fs object upon failure, but the FileSystem may be re-initialized every
> time the job gets restarted.
> A few evidence I observed:
> 1. When I set the connection pool limit to 128, and below commands shows 128
> connections are stuck in CLOSE_WAIT state.
> !Screen Shot 2016-09-20 at 2.49.14 PM.png|align=left, vspace=5!
> 2. task manager logs indicates that state backend file system consistently
> getting initialized upon job restarting.
> !Screen Shot 2016-09-20 at 2.49.32 PM.png!
> 3. Log indicates there is NPE during cleanning up of stream task which was
> caused by “Timeout waiting for connection from pool” exception when trying to
> create a directory in S3 bucket.
> 2016-09-02 08:17:50,886 ERROR
> org.apache.flink.streaming.runtime.tasks.StreamTask - Error during cleanup of
> stream task
> java.lang.NullPointerException
> at
> org.apache.flink.streaming.runtime.tasks.OneInputStreamTask.cleanup(OneInputStreamTask.java:73)
> at
> org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:323)
> at org.apache.flink.runtime.taskmanager.Task.run(Task.java:589)
> at java.lang.Thread.run(Thread.java:745)
> 4.It appears StreamTask from invoking checkpointing operation, to handling
> failure, there is no logic associated with closing Hadoop File System object
> (which internally includes S3 aws client object), which resides in
> HadoopFileSystem.java.
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