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From "Holden Robbins (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2990) Ability to thread task execution
Date Tue, 11 Mar 2008 00:02:46 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2990?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12577256#action_12577256
] 

Holden Robbins commented on HADOOP-2990:
----------------------------------------

Useful to know thanks.  

Is this the Multi-threaded mapper you're refering to?
http://issues.apache.org/jira/browse/HADOOP-811

Did it not make it into the code base?  Any reason why?


> Ability to thread task execution
> --------------------------------
>
>                 Key: HADOOP-2990
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2990
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: mapred
>         Environment: All
>            Reporter: Holden Robbins
>   Original Estimate: 48h
>  Remaining Estimate: 48h
>
> Currently Hadoop spawns a single threaded JVM for each task.  While good for many tasks,
this does not maximize resource usage for slaves that have many cores (machines with more
cores are getting more cost effective everyday) _and_ are running jobs that require many gigabytes
of read-only in-memory resources to maximize throughput.  Running in separate JVMs requires
redundantly loading large amounts of data, reducing the possible number of parallel tasks
that can run per a machine even though more cpus are available.
> Adding this ability will give hadoop users the flexibility to balance their need for
maximizing memory usage & throughput and task segmentation.
> Note: This is a blocking bug in porting processes over to hadoop for my own organization.
 I am testing a patch for this now that leaves the existing behavior for single threaded operation
in-tact.  All synchronization is done through wrapper classes and helper methods and should
not add any overhead to non-threaded processes.

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