FAQ

On Sep 25, 2007, at 10:09 AM, Michael Bieniosek wrote:

For our CPU-bound application, I set the value of
mapred.tasktracker.tasks.maximum (number of map tasks per
tasktracker) equal to the number of CPUs on a tasktracker.
Unfortunately, I think this value has to be set per cluster, not
per machine. This is okay for us because our machines have similar
hardware, but it might be a problem if your machines have different
numbers of CPUs.
I did some experimentation with the number of tasks per machine on a
set of quad core boxes. I couldn't figure out how to change this
value without stopping the cluster and restarting it, and I also
couldn't figure out how to tune it on a per machine basis (though it
didn't matter much for me either).

My test had no reduce phase, so I simply set the reduce count to 1
per machine for all the tests. On the quad core boxes, 5 map tasks
per machine actually performed the best, but only marginally better
than 4 map tasks (about 4% with just one box in the cluster, 2% with
4 boxes). Six tasks started to trend back in the other direction.
I created HADOOP-1245 a long time ago for this problem, but I've
since heard that hadoop uses only the cluster value for maps per
tasktracker, not the hybrid model I describe. In any case, I never
did any work on fixing it because I don't need heterogeneous clusters.

-Michael

On 9/25/07 9:37 AM, "Ted Dunning" wrote:
On 9/25/07 9:27 AM, "Bob Futrelle" wrote:


How does Hadoop handle multi-core CPUs? Does each core run a
distinct copy
of the mapped app? Is this automatic, or need some configuration,
or what?
Works fine. You need to tell it how many maps to run per machine.
I expect
that this can be tuned per machine.
Or should I just spread Hadoop over some friendly machines already
in my
College, buying nothing?
Or both? You will get interesting results all three ways.

Search Discussions

Discussion Posts

Previous

Follow ups

Related Discussions

Discussion Navigation
viewthread | post
posts ‹ prev | 9 of 11 | next ›
Discussion Overview
groupcommon-user @
categorieshadoop
postedSep 10, '07 at 11:56p
activeSep 25, '07 at 7:35p
posts11
users7
websitehadoop.apache.org...
irc#hadoop

People

Translate

site design / logo © 2022 Grokbase