A reporter thread during the reduce stage for a long running line

[Saptarshi Guha <sa...@gmail.com>]

Hello,
  Sorry for the puzzling subject. I have a single long running
/statement/ in my reduce method, so the the framework might assume my
reduce is not responding and kill it.
I solved the problem in the map method by subclassing MapRunner, and
running a thread which calls reporter.progress() every minute or so.
However the same thread does not run during the reduce (i checked this
by setting a status string in the thread which  did not appear (on the
Jobtracker website) during the reduce stage but did appearing during
the map stage).

Hadoop v.0.20 appears to solve this by having separate run methods for
both Map and Reduce, however I'm using v 0.19.
I scanned the Streaming source and it only subclasses MapRunner, so I
assume it to has the same limitation (probably wrong, if so can
someone point me to the location?)

Is there a way around this, /without/ starting a thread in the reduce function?
Hadoop v 0.19

Many thanks
Saptarshi




-- 
Saptarshi Guha - saptarshi.guha@gmail.com

Re: A reporter thread during the reduce stage for a long running line

[Arun C Murthy <ac...@yahoo-inc.com>]

On Jan 9, 2009, at 12:09 AM, Saptarshi Guha wrote:

> Hello,
>  Sorry for the puzzling subject. I have a single long running
> /statement/ in my reduce method, so the the framework might assume my
> reduce is not responding and kill it.
> I solved the problem in the map method by subclassing MapRunner, and
> running a thread which calls reporter.progress() every minute or so.
> However the same thread does not run during the reduce (i checked this
> by setting a status string in the thread which  did not appear (on the
> Jobtracker website) during the reduce stage but did appearing during
> the map stage).
>
> Hadoop v.0.20 appears to solve this by having separate run methods for
> both Map and Reduce, however I'm using v 0.19.
> I scanned the Streaming source and it only subclasses MapRunner, so I
> assume it to has the same limitation (probably wrong, if so can
> someone point me to the location?)
>
> Is there a way around this, /without/ starting a thread in the  
> reduce function?
> Hadoop v 0.19
>

If you are _really_ sure you do not want the reducer to get killed  
regardless of whether it's making progress or not, set  
mapred.task.timeout to 0 in your JobConf.

Please be aware that this will mean the framework cannot detect if  
your mapper/reducer tasks are hung...

Arun