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https://issues.apache.org/jira/browse/HADOOP-13826?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15744784#comment-15744784
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Steve Loughran commented on HADOOP-13826:
-----------------------------------------

bq. COPY is completely server-side and is thus generally much less 
resource-intensive

Yes: it keeps TCP channel open, but consumes no bandwidth. In contrast, the 
more PUTs you have, the longer each one takes. This is why the Huge* tests all 
have to run sequentially. The new test here doesn't, but it still need to be a 
scale test to make it optional (it's still slow, doing big uploads, ...)

> S3A Deadlock in multipart copy due to thread pool limits.
> ---------------------------------------------------------
>
>                 Key: HADOOP-13826
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13826
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: fs/s3
>    Affects Versions: 2.7.3
>            Reporter: Sean Mackrory
>            Assignee: Sean Mackrory
>            Priority: Critical
>         Attachments: HADOOP-13826.001.patch, HADOOP-13826.002.patch, 
> HADOOP-13826.003.patch
>
>
> In testing HIVE-15093 we have encountered deadlocks in the s3a connector. The 
> TransferManager javadocs 
> (http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/s3/transfer/TransferManager.html)
>  explain how this is possible:
> {quote}It is not recommended to use a single threaded executor or a thread 
> pool with a bounded work queue as control tasks may submit subtasks that 
> can't complete until all sub tasks complete. Using an incorrectly configured 
> thread pool may cause a deadlock (I.E. the work queue is filled with control 
> tasks that can't finish until subtasks complete but subtasks can't execute 
> because the queue is filled).{quote}



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