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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 Mon, 12 Dec 2016 22:51:58 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-13826?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15743421#comment-15743421

Thomas Demoor commented on HADOOP-13826:

[~mackrorysd] your last patch seems simple but I think it might do the trick. I like simple

{{putObject()}} uses the (unbounded) TransferManager, {{putObjectDirect()}}  and {{uploadPart()}}
use the bounded threadpool so I think the (potentially) memory intensive parts are nicely
isolated and under control.
My only slight concern is that now both pools can have {{MAX_THREADS}} active. From my reading
of the code, both threadpools cannot be doing large object PUTs at the same time (an instance
of s3a uses the block-based uploads or the regular S3AOutputstream, never both at the same
time). What is possible, is that during a large block-based upload, which is saturating the
bounded executor, another client thread might {{rename}} a directory, invoking a lot of parallel
copies, hence saturating the TransferManager. But copies are are not data-intensive (see below)
so I assume this is manageable.

I like [~stevel@apache.org]'s ideas for further separating out the different types of operations,
but have one remark: for me COPY is not similar to PUT. COPY is completely server-side and
is thus generally much less resource-intensive and much quicker than PUT (the smaller your
bandwidth to S3, the bigger the difference becomes).

> 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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