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From "Weichen Ye (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-12590) A solution for data skew in HBase-Mapreduce Job
Date Thu, 27 Nov 2014 01:59:12 GMT
Weichen Ye created HBASE-12590:

             Summary: A solution for data skew in HBase-Mapreduce Job 
                 Key: HBASE-12590
                 URL: https://issues.apache.org/jira/browse/HBASE-12590
             Project: HBase
          Issue Type: Improvement
          Components: mapreduce
    Affects Versions: 2.0.0
            Reporter: Weichen Ye

1, Motivation
In production environment, data skew is a very common case. A HBase table always contains
a lot of small regions and several large regions. Small regions waste a lot of computing resources.
If we use a job to scan a table with 3000 small regions, we need a job with 3000 mappers.
Large regions always block the job. If in a 100-region table, one region is far larger then
the other 99 regions. When we run a job with the table as input, 99 mappers will be completed
very quickly, and we need to wait for the last mapper for a long time.

2, Configuration
Add two new configuration. 
hbase.mapreduce.split.autobalance = true means enabling the “auto balance” in HBase-MapReduce
jobs. The default value is false. 
hbase.mapreduce.split.targetsize = 1073741824 (default 1GB). The target size of mapreduce
If a region size is large than the target size, cut the region into two split.If the sum of
several small continuous region size less than the target size, combine these regions into
one split.

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