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From rishi pathak <mailmaverick...@gmail.com>
Subject Re: Draining/Decommisioning a tasktracker
Date Sat, 29 Jan 2011 13:37:13 GMT
    Here is a description of what we are trying to achieve(whether it is
possible or not is still not cear):
We have large computing clusters used majorly  for MPI jobs. We use
PBS/Torque and Maui for resource allocation and scheduling.
At most times utilization is very high except for very small resource
pockets of say 16 cores for 2-5 Hrs. We are trying establish feasibility of
using these small(but fixed sized) resource pockets for nutch crawls. Our
configuration is:

# Hadoop 0.20.2 (packaged with nutch)
#Lustre parallel filesystem for data storage

We have JT running on one of the login nodes at all times.
Request for resource (nodes=16, walltime=05 Hrs.) is made using batch system
and as a part of job TTs are provisioned. The problem is, when a job
expires, user processes are cleaned up and thus TT gets killed. With that,
completed and running map/reduce tasks for nutch job are killed and are
rescheduled. Solution could be as we see it:

1. As the filesystem is shared(& persistent),  restart tasks on another TT
and make intermediate task data available. i.e. sort of checkpointing.
2. TT draining - based on a speculative time for task completion, TT whose
walltime is nearing expiry will go into draining mode.i.e. no new tasks will
be scheduled on that TT.

For '1', it is very far fetched(we are no Hadoop expert)
'2' seems to be a more sensible approach.

Using exclude list for TT will not help as Koji has already mentioned
We looked into capacity scheduler but did'nt find any pointers. Phil, what
version of hadoop
have these hooks in scheduler.

On Sat, Jan 29, 2011 at 3:34 AM, phil young <phil.wills.young@gmail.com>wrote:

> There are some hooks available in the schedulers that could be useful also.
> I think they were expected to be used to allow you to schedule tasks based
> on load average on the host, but I'd expect you can customize them for your
> purpose.
> On Fri, Jan 28, 2011 at 6:46 AM, Harsh J <qwertymaniac@gmail.com> wrote:
> > Moving discussion to the MapReduce-User list:
> > mapreduce-user@hadoop.apache.org
> >
> > Reply inline:
> >
> > On Fri, Jan 28, 2011 at 2:39 PM, rishi pathak <mailmaverick666@gmail.com
> >
> > wrote:
> > > Hi,
> > >        Is there a way to drain a tasktracker. What we require is not to
> > > schedule any more map/red tasks onto a tasktracker(mark it offline) but
> > > still the running tasks should not be affected.
> >
> > You could simply shut the TT down. MapReduce was designed with faults
> > in mind and thus tasks that are running on a particular TaskTracker
> > can be re-run elsewhere if they failed. Is this not usable in your
> > case?
> >
> > --
> > Harsh J
> > www.harshj.com
> >

Rishi Pathak
National PARAM Supercomputing Facility
C-DAC, Pune, India

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