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From "Koji Noguchi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-2011) Reduce number of getFileStatus call made from every task(TaskDistributedCache) setup
Date Mon, 16 Aug 2010 16:36:18 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2011?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12898981#action_12898981

Koji Noguchi commented on MAPREDUCE-2011:

MAPREDUCE-1901 has a detail proposal of how to handle distributed cache better for those loaded
by jobclient (-libjars).
As part of it, it mentions 

The TaskTracker, on being requested to run a task requiring CAR resource md5_F checks whether
md5_F is localized.

    * If md5_F is already localized - then nothing more needs to be done. the localized version
is used by the Task
    * If md5_F is not localized - then its fetched from the CAR repository

This Jira is basically almost asking the same except for asking to use existing mtime instead
of a new md5_F proposed.
Just to reduce the mtime/getFileStatus calls, mtime check is enough and can keep the change

> Reduce number of getFileStatus call made from every task(TaskDistributedCache) setup
> ------------------------------------------------------------------------------------
>                 Key: MAPREDUCE-2011
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2011
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: distributed-cache
>            Reporter: Koji Noguchi
> On our cluster, we had jobs with 20 dist cache and very short-lived tasks resulting in
500 map tasks launched per second resulting in  10,000 getFileStatus calls to the namenode.
 Namenode can handle this but asking to see if we can reduce this somehow.  

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