DistRaid map tasks have large variance in running times
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Key: MAPREDUCE-1838
URL: https://issues.apache.org/jira/browse/MAPREDUCE-1838
Project: Hadoop Map/Reduce
Issue Type: Improvement
Components: contrib/raid
Affects Versions: 0.20.1
Reporter: Ramkumar Vadali
Priority: Minor
HDFS RAID uses map-reduce jobs to generate parity files for a set of source
files. Each map task gets a subset of files to operate on. The current code
assigns files by walking through the list of files given in the constructor of
DistRaid
The problem is that the list of files given to the constructor has the order of
(pretty much) the directory listing. When a large number of files is added,
files in that order tend to have the same size. Thus a map task can end up with
large files where as another can end up with small files, increasing the
variance in run times.
We could do smarter assignment by using the file sizes.
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