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From Stack <st...@duboce.net>
Subject Re: Reading in parallel from table's regions in MapReduce
Date Tue, 04 Sep 2012 19:13:27 GMT
On Tue, Sep 4, 2012 at 8:17 AM, Ioakim Perros <imperros@gmail.com> wrote:
> Hello,
> I would be grateful if someone could shed a light to the following:
> Each M/R map task is reading data from a separate region of a table.
> From the jobtracker 's GUI, at the map completion graph, I notice that
> although data read from mappers are different, they read data sequentially -
> like the table has a lock that permits only one mapper to read data from
> every region at a time.

Your mapreduce job is actually running on the cluster and not in a
single thread local (as Jerry hints above).

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