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From "Rajesh Balamohan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (TEZ-3103) Shuffle can hang when memory to memory merging enabled
Date Thu, 11 Feb 2016 22:00:19 GMT

    [ https://issues.apache.org/jira/browse/TEZ-3103?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15143583#comment-15143583

Rajesh Balamohan commented on TEZ-3103:

+1. lgtm. Thanks [~jlowe]

> Shuffle can hang when memory to memory merging enabled
> ------------------------------------------------------
>                 Key: TEZ-3103
>                 URL: https://issues.apache.org/jira/browse/TEZ-3103
>             Project: Apache Tez
>          Issue Type: Bug
>    Affects Versions: 0.7.0
>            Reporter: Jason Lowe
>            Assignee: Jason Lowe
>            Priority: Critical
>         Attachments: TEZ-3103.001.patch, TEZ-3103.002.patch
> The shuffle process can hang when memory to memory merging is enabled.  As the memory-to-memory
merge progresses it closes out the input segments which in turn lowers the commitMemory associated
with those segments.  However when the merge completes it fails to increase the commitMemory
accordingly for the resulting merged segment.  This effectively "leaks" shuffle memory, and
we can end up in a situation where there's insufficient memory to perform any more in-memory
shuffles but commitMemory is too low to trigger a merge.  All the fetcher threads eventually
end up waiting on the merge that will never occur, and the shuffle hangs.

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