Hi Schubert, Currently, combiners use the OutputKeyComparator and not OutputValueGroupingComparator.
If you think this functionality is very useful to you, you could raise a Jira for the same and discuss it there. Needless to say, you could always contribute your patch for the Jira too :) Jothi On 5/11/09 5:12 PM, "zsongbo" <zson...@gmail.com> wrote: > 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 >> >>
