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From Pankil Doshi <forpan...@gmail.com>
Subject Re: Map-Reduce Slow Down
Date Mon, 13 Apr 2009 04:33:26 GMT
Your data is too small I guess for 15 clusters ..So it might be overhead
time of these clusters making your total MR jobs more time consuming.
I guess you will have to try with larger set of data..

Pankil
On Sun, Apr 12, 2009 at 6:54 PM, Mithila Nagendra <mnagendr@asu.edu> wrote:

> Aaron
>
> That could be the issue, my data is just 516MB - wouldn't this see a bit of
> speed up?
> Could you guide me to the example? I ll run my cluster on it and see what I
> get. Also for my program I had a java timer running to record the time
> taken
> to complete execution. Does Hadoop have an inbuilt timer?
>
> Mithila
>
> On Mon, Apr 13, 2009 at 1:13 AM, Aaron Kimball <aaron@cloudera.com> wrote:
>
> > Virtually none of the examples that ship with Hadoop are designed to
> > showcase its speed. Hadoop's speedup comes from its ability to process
> very
> > large volumes of data (starting around, say, tens of GB per job, and
> going
> > up in orders of magnitude from there). So if you are timing the pi
> > calculator (or something like that), its results won't necessarily be
> very
> > consistent. If a job doesn't have enough fragments of data to allocate
> one
> > per each node, some of the nodes will also just go unused.
> >
> > The best example for you to run is to use randomwriter to fill up your
> > cluster with several GB of random data and then run the sort program. If
> > that doesn't scale up performance from 3 nodes to 15, then you've
> > definitely
> > got something strange going on.
> >
> > - Aaron
> >
> >
> > On Sun, Apr 12, 2009 at 8:39 AM, Mithila Nagendra <mnagendr@asu.edu>
> > wrote:
> >
> > > Hey all
> > > I recently setup a three node hadoop cluster and ran an examples on it.
> > It
> > > was pretty fast, and all the three nodes were being used (I checked the
> > log
> > > files to make sure that the slaves are utilized).
> > >
> > > Now I ve setup another cluster consisting of 15 nodes. I ran the same
> > > example, but instead of speeding up, the map-reduce task seems to take
> > > forever! The slaves are not being used for some reason. This second
> > cluster
> > > has a lower, per node processing power, but should that make any
> > > difference?
> > > How can I ensure that the data is being mapped to all the nodes?
> > Presently,
> > > the only node that seems to be doing all the work is the Master node.
> > >
> > > Does 15 nodes in a cluster increase the network cost? What can I do to
> > > setup
> > > the cluster to function more efficiently?
> > >
> > > Thanks!
> > > Mithila Nagendra
> > > Arizona State University
> > >
> >
>

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