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From Amandeep Khurana <ama...@gmail.com>
Subject Re: getSplits() in TableInputFormatBase
Date Sun, 11 Apr 2010 08:53:42 GMT
How many regions do you have?


Amandeep Khurana
Computer Science Graduate Student
University of California, Santa Cruz


On Sun, Apr 11, 2010 at 1:39 AM, john smith <js1987.smith@gmail.com> wrote:

> Amandeep ,
>
> Thanks for the explanation . What is the default value to the num of maps ?
> Is it not equal to the num of regions ?
>
> Right now I am running HBase in pseudo distributed mode . If I set num of
> map tasks to 100000 (some big num)..
>
> I get numSplits=1
>
> If I dont set any thing .. numSplits =2;
>
>
> Can you explain this.
>
> Thanks
> j.S
>
> On Sun, Apr 11, 2010 at 1:50 PM, Amandeep Khurana <amansk@gmail.com>
> wrote:
>
> > If you set the number of map tasks as a higher number than the number of
> > regions (I generally set it to 100000 or something like that), the number
> > of
> > splits = number of regions. If you keep it lower, then it combines
> regions
> > in a single split.
> >
> >
> > Amandeep Khurana
> > Computer Science Graduate Student
> > University of California, Santa Cruz
> >
> >
> > On Sun, Apr 11, 2010 at 1:15 AM, john smith <js1987.smith@gmail.com>
> > wrote:
> >
> > > Amandeep,
> > >
> > > I guess that is not true ,.. See the explanation as in docs ..
> > >
> > >
> > > "Splits are created in number equal to the smallest between numSplits
> and
> > > the number of HRegion<
> > >
> >
> http://hadoop.apache.org/hbase/docs/r0.20.3/api/org/apache/hadoop/hbase/regionserver/HRegion.html
> > > >s
> > > in the table. If the number of splits is smaller than the number of
> > > HRegion<
> > >
> >
> http://hadoop.apache.org/hbase/docs/r0.20.3/api/org/apache/hadoop/hbase/regionserver/HRegion.html
> > > >s
> > > then splits are spanned across multiple
> > > HRegion<
> > >
> >
> http://hadoop.apache.org/hbase/docs/r0.20.3/api/org/apache/hadoop/hbase/regionserver/HRegion.html
> > > >s
> > > and are grouped the most evenly possible. In the case splits are uneven
> > the
> > > bigger splits are placed first in the InputSplit array.  "
> > >
> > >
> > > depending on whether numSplits < (or >)  num of regions .. it choses
> real
> > > number of splits and the same is done in the code
> > >
> > > // Code
> > >  int realNumSplits = numSplits > startKeys.length? startKeys.length:
> > > numSplits;
> > >
> > > Here startKeys.length is the number of regions...
> > >
> > > Am I true?
> > >
> > > Thanks
> > > j.S
> > >
> > >
> > >
> > > On Sun, Apr 11, 2010 at 1:33 PM, Amandeep Khurana <amansk@gmail.com>
> > > wrote:
> > >
> > > > The number of splits is equal to the number of regions...
> > > >
> > > >
> > > >
> > > > On Sun, Apr 11, 2010 at 12:54 AM, john smith <js1987.smith@gmail.com
> >
> > > > wrote:
> > > >
> > > > > Hi ,
> > > > >
> > > > > In the method  "public org.apache.hadoop.mapred.InputSplit[]
> > > *getSplits*
> > > > > (org.apache.hadoop.mapred.JobConf job,
> > > > >
> > > > >                                                       int
> numSplits)
> > "
> > > > >
> > > > > how is the "numSplits" decided ? I've seen differnt values of
> > > > > numSplits for different MR jobs . Any reason for this ?
> > > > >
> > > > > Also what if I ignore numsplits and always split at region
> > > > > boundaries.I guess that , splitting at region boundaries makes more
> > > > > sense and improves some what data locality.
> > > > >
> > > > > Any comments on the above statement?
> > > > >
> > > > > Thanks
> > > > >
> > > > > j.S
> > > > >
> > > >
> > >
> >
>

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