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From "Joydeep Sen Sarma (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-2980) slow reduce copies - map output locations not being fetched even when map complete
Date Sat, 08 Mar 2008 03:03:46 GMT
slow reduce copies - map output locations not being fetched even when map complete
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                 Key: HADOOP-2980
                 URL: https://issues.apache.org/jira/browse/HADOOP-2980
             Project: Hadoop Core
          Issue Type: Bug
    Affects Versions: 0.15.3
            Reporter: Joydeep Sen Sarma


maps are long finished. reduces are stuck looking for map locations. they make progress -
but slowly. it almost seems like they get new map locations every minute or so:

2008-03-07 18:50:52,737 INFO org.apache.hadoop.mapred.ReduceTask: task_200803041231_3586_r_000021_0
done copying task_200803041231_3586_m_004620_0 output from hadoop082.sf2p.facebook.com..
2008-03-07 18:50:53,733 INFO org.apache.hadoop.mapred.ReduceTask: task_200803041231_3586_r_000021_0:
Got 0 new map-outputs & 0 obsolete map-outputs from tasktracker and 0 map-outputs from
previous failures
2008-03-07 18:50:53,733 INFO org.apache.hadoop.mapred.ReduceTask: task_200803041231_3586_r_000021_0
Got 0 known map output location(s); scheduling...
...
2008-03-07 18:51:49,767 INFO org.apache.hadoop.mapred.ReduceTask: task_200803041231_3586_r_000021_0
Got 50 known map output location(s); scheduling...
2008-03-07 18:51:49,767 INFO org.apache.hadoop.mapred.ReduceTask: task_200803041231_3586_r_000021_0
Scheduled 41 of 50 known outputs (0 slow hosts and 9 dup hosts)

they get about 50 locations at a time and this 1 minute delay pattern is surprisingly common
..

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