See Hadoop definitive guide and search for chapter on Hadoop features On Fri, Aug 17, 2012 at 6:20 PM, Manoj Khangaonkar <khangaon...@gmail.com>wrote:
> One usage of these is in a secondary sort , which is used , when you > want the output values from Map sorted (within a key). > > You implement a KeyComparator and tell mapreduce to use it to order > the keys using a composite key. > > To ensure that during partioning & Grouping , all the records for a > key go to the same reducer > you need to define and set a Partitioner and ValueGroupingComparator. > > search for Secondary Sort for more on this topic > > regards > > MJ > > On Fri, Aug 17, 2012 at 12:00 PM, Anbarasan Murthy > <anbu992...@hotmail.com> wrote: > > Hi, > > > > I have a question in mapreduce api. > > > > Would like to know the significance of the following items under jobconf > > class. > > ValueGroupingComparator > > KeyComparator > > > > > > > > Thanks, > > Anbu. > > > > -- > http://khangaonkar.blogspot.com/ >
