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From "Jeff Hammerbacher" <jeff.hammerbac...@gmail.com>
Subject Re: Appropriate use of Hadoop for non-map/reduce tasks?
Date Sat, 22 Dec 2007 19:40:44 GMT
from my understanding, the map/reduce codebase grew out of the codebase for
"the borg", google's system for managing long-running processes.  we could
definitely use this sort of functionality, and the jobtracker/tasktracker
paradigm goes part of the way there.  sqs really helps when you want to run
a set of recurring, dependent processes (a problem our group definitely
needs to solve), but it doesn't really seem to address the issue of managing
those processes when they're long-lived.

for instance, when we deploy our search servers, we have a script that
basically says "daemonize this process on this many boxes, and if it enters
a condition that doesn't look healthy, take this action (like restart, or
rebuild the index, etc.)".  given how hard-coded the task-type is into
map/reduce (er, "map" and "reduce"), it's hard to specify new types of error
conditions and running conditions for your processes.  also, the jobtracker
doesn't have any high availability guarantees, so you could run into a
situation where your processes are fine but the jobtracker goes down.
 zookeeper could help here.  it'd be sweet if hadoop could handle this
long-lived process management scenario.

kirk, i'd be interested in hearing more about your processes and the
requirements you have of your process manager.  we're exploring other
solutions to this problem and i'd be happy to connect you with the folks
here who are thinking about the issue.


On Dec 21, 2007 12:42 PM, John Heidemann <johnh@isi.edu> wrote:

> On Fri, 21 Dec 2007 12:24:57 PST, John Heidemann wrote:
> >On Thu, 20 Dec 2007 18:46:58 PST, Kirk True wrote:
> >>Hi all,
> >>
> >>A lot of the ideas I have for incorporating Hadoop into internal
> projects revolves around distributing long-running tasks over multiple
> machines. I've been able to get a quick prototype up in Hadoop for one of
> those projects and it seems to work pretty well.
> >>...
> >He's not saying "is Hadoop optimal" for things that aren't really
> >map/reduce, but "is it reasonable" for those things?
> >(Kirk, is that right?)
> >...
> Sorry to double reply, but I left out my comment to (my view of) Kirk's
> question.
> In addition to what Ted said, I'm not sure how well Hadoop works with
> long-running jobs, particuarlly how well that interacts with its fault
> tolerance code.
> And more generally, if you're not doing map/reduce than you'd probably
> have to build your own fault tolerance methods.
>   -John Heidemann

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