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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-248) locating map outputs via random probing is inefficient
Date Thu, 25 Jan 2007 16:51:49 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-248?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Devaraj Das updated HADOOP-248:

    Attachment: 248-initial8.patch

This patch does better failure handling. It saves the location of a failed map output fetch
in a hashmap for later retrial. Also, it has logic which makes it prefer a newer location
to the saved one.

> locating map outputs via random probing is inefficient
> ------------------------------------------------------
>                 Key: HADOOP-248
>                 URL: https://issues.apache.org/jira/browse/HADOOP-248
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: mapred
>    Affects Versions: 0.2.1
>            Reporter: Owen O'Malley
>         Assigned To: Devaraj Das
>         Attachments: 248-initial7.patch, 248-initial8.patch
> Currently the ReduceTaskRunner polls the JobTracker for a random list of map tasks asking
for their output locations. It would be better if the JobTracker kept an ordered log and the
interface was changed to:
> class MapLocationResults {
>    public int getTimestamp();
>    public MapOutputLocation[] getLocations();
> }
> interface InterTrackerProtocol {
>   ...
>   MapLocationResults locateMapOutputs(int prevTimestamp);
> } 
> with the intention that each time a ReduceTaskRunner calls locateMapOutputs, it passes
back the "timestamp" that it got from the previous result. That way, reduces can easily find
the new MapOutputs. This should help the "ramp up" when the maps first start finishing.

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