-Re: Reduce Task Clarification
Harsh J 2013-08-14, 05:28
Are you looking to do a secondary sort under a grouped key?
A reduce() is called once for each globally unique map() emitted key,
along with all values grouped for it. To sort the grouped data, you
need to use a separate sort comparator and perform the 'secondary
On Wed, Aug 14, 2013 at 1:21 AM, Sam Garrett <[EMAIL PROTECTED]> wrote:
> I am working on a MapReduce job where I would like to have the output sorted
> by a LongWritable value. I read the Anatomy of a MapReduce Run in the
> Definitive Guide and it didn't say explicitly whether reduce() gets called
> only once per map output key. If it does get called only once I was thinking
> that I could use this:
> to do the sorting.
> Thank you for your time.
> Sam Garrett
> ActionX, NYC