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From "Bryan Duxbury (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5664) Use of ReentrantLock.lock() in MapOutputBuffer takes up too much cpu time
Date Mon, 13 Apr 2009 23:55:14 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5664?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12698594#action_12698594

Bryan Duxbury commented on HADOOP-5664:

I'm using YourKit in sampling mode, so the overhead incurred by the profiler should be close
to zero. 

I understand why we should try to avoid extra buffers in general, but is this a place where
we could introduce a configurable buffer? Maybe if the count is set to 1, we skip the buffer,
otherwise push to the spill thread only every N writes?

I'm not sure if synchronized() will solve this problem or not. Is there an easy way to test

> Use of ReentrantLock.lock() in MapOutputBuffer takes up too much cpu time
> -------------------------------------------------------------------------
>                 Key: HADOOP-5664
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5664
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>    Affects Versions: 0.19.1
>            Reporter: Bryan Duxbury
>            Priority: Minor
> In examining a profile of one of my mappers today, I noticed that the method ReentrantLock.lock()
in MapTask$MapOutputBuffer seems to be taking up ~11 seconds out of around 100 seconds total.
It seems like 10% is an awfully large amount of time to spend in this lock. 

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