Thanks Jothi, For example, I have a dataset with map key="city+userid+time". The output of mapper are sorted by this map key.
Than, I group the reduce output according to "city+userid" by define my OutputValueGroupingComparator which just compare "city+userid" in the mapkey. I still want the output are sorted by time in each group. It works fine. But to improve the performance, I want to use combiner which should also group as "city+userid", but sorted by "city+userid+time". I do not know if this requirement is reasonable. Schubert On Thu, May 7, 2009 at 7:53 PM, Jothi Padmanabhan <joth...@yahoo-inc.com>wrote: > OutputValueGroupingComparator is used only at the reducer. AFAIK, I do not > think you can have a different comparator for combiners. > > Jothi > > > On 5/7/09 3:32 PM, "zsongbo" <zson...@gmail.com> wrote: > > > Hi all, > > I have a application want the rules of sorting and grouping use > > different Comparator. > > > > I had tested 0.19.1 and 0.20.0 about this function, but both do not work > for > > Combiner. > > > > In 0.19.1, I use job.setOutputValueGroupingComparator(), and > > in 0.20.0, I use job.setGroupingComparatorClass() > > > > This function is ok for reduce phase, the reduce phase can group the keys > by > > above Comparator, and sort by default comparator of the key class. > > > > But I want the combiner can use a separator comparator for group, > different > > from sorting, is it possible? > > > > Schubert > >
