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From Albert Shau <as...@yahoo-inc.com>
Subject region, regionserver questions
Date Thu, 02 Dec 2010 22:26:03 GMT

I'm doing a distributed scan of an hbase table using map-reduce by taking all the regions
belonging to a regionserver, and then assigning those regions to a mapper (so there's 1 mapper
per regionserver, and each mapper only talks to one regionserver).  However, doing it this
way I'm getting some data skew.  For example, I have 2 tables U and T.  Each regionserver
may have 30 regions, but one regionserver might have 10 regions from table U while another
regionserver might have 25 regions from table U.  Is there a way to balance regions per table
per regionserver (so that each regionserver has 15 regions from table U for example)?  Or
should I just not worry about trying to have each individual mapper only talk to one regionserver?

Also, how do regions get assigned to regionservers?  Is it based on data locality?  Region
start/end keys?  Randomly?


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