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From "Thomas Demoor (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-13826) S3A Deadlock in multipart copy due to thread pool limits.
Date Wed, 30 Nov 2016 20:33:59 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-13826?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15709695#comment-15709695
] 

Thomas Demoor commented on HADOOP-13826:
----------------------------------------

I think [~mackrorysd]'s implementation is heading in the right direction.

Some questions / suggestions:
* The {{controlTypes}} do not have a large memory and bandwidth impact as they carry little
payload. Consequently, I think we can allow a lot of active threads here and the waiting room
can be unbounded. I hope this would fix the issues [~mackrorysd] is still encountering. (In
contrast to my earlier thinking above, I don't think the number of active threads needs to
be shared between the two types, it seems unlikely that {{controlTypes}} will use significant
resources) 
* The {{subTaskTypes}} have the potential to overwhelm memory and bandwidth usage and should
thus be run from the  bounded threadpool. We need to take care that all relevant classes are
captured here.
* I am not 100% sure if what I propose here would eliminate all deadlocks. I do not understand
the deadlock scenario entirely (yet) from the discussion above. If you would have more insight
please help me out.

> 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
>
>
> 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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