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From "Sandy Ryza (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-4907) TrackerDistributedCacheManager issues too many getFileStatus calls
Date Fri, 28 Dec 2012 22:06:12 GMT
Sandy Ryza created MAPREDUCE-4907:

             Summary: TrackerDistributedCacheManager issues too many getFileStatus calls
                 Key: MAPREDUCE-4907
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4907
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: mrv1, tasktracker
    Affects Versions: 1.1.1
            Reporter: Sandy Ryza
            Assignee: Sandy Ryza

TrackerDistributedCacheManager issues a number of redundant getFileStatus calls when determining
the timestamps and visibilities of files in the distributed cache.  300 distributed cache
files deep in the directory structure can hammer HDFS with a couple thousand requests.

A couple optimizations can reduce this load:
1. determineTimestamps and determineCacheVisibilities both call getFileStatus on every file.
 We could cache the results of the former and use them for the latter.
2. determineCacheVisibilities needs to check that all ancestor directories of each file have
execute permissions for everyone.  This currently entails a getFileStatus on each ancestor
directory for each file.  The results of these getFileStatus calls could be cached as well.

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