Hi and thank you for the answers. I didn't check the email and now I see 7 answers. It is really great.
Let me explain in more details why I am asking so strange question :-) As I wrote before I write to HBase using Hadoop Job. Actually the writing process executes in reducers part of HADOOP job. Assuming that I have 3 reducers (all of them writes to HBase) and suppose 1 reducer and 3 reducer has the same key. In this case I need to check: does HBase already contains such key ( it required select operation from HBase). If yes I have to merge already inserted record and after that writes it back to HBase. BUT in my case information organized in such way that I have no problem with the same keys. So I can save expensive HBase select operation , meaning using only insert operations. But in order to use only insert operation I need to know that every and every reducer have unique output key ( K3 is unique output key for every and every reducer) input: InputFormat<K1,V1> mapper: Mapper<K1,V1,K2,V2> combiner: Reducer<K2,V2,K2,V2> reducer: Reducer<K2,V2,K3,V3> output: RecordWriter<K3,V3> On Thu, Jun 10, 2010 at 12:40 AM, James Seigel <[email protected]> wrote: > Oleg, > > Are you wanting to have them in different reducers? If so then you can > write a Comparable object to make that happen. > > If you want them to be on the same reducer, then that is what hadoop will > do. > > :) > > > On 2010-06-09, at 3:06 PM, Ted Yu wrote: > > > Can you disclose more about how K3 is generated. > > From your description below, it is possible. > > > > On Wed, Jun 9, 2010 at 1:17 AM, Oleg Ruchovets <[email protected]> > wrote: > > > >> Hi , > >> My hadoop job writes results of map/reduce to HBase. > >> I have 3 reducers. > >> > >> Here is a sequence of input and output parameters for Mapper , Combiner > and > >> Reducer > >> *input: InputFormat<K1,V1> > >> mapper: Mapper<K1,V1,K2,V2> > >> combiner: Reducer<K2,V2,K2,V2> > >> reducer: Reducer<K2,V2,K3,V3> > >> output: RecordWriter<K3,V3> > >> > >> *My question: > >> Is it possible that more than one reducer has the same output key K3. > >> Meaning in case I have 3 reducers is it possible that > >> reducer1 K3 -* 1* , V3 [1,2,3] > >> reducer2 K3 - 2 , V3 [5,6,9] > >> reducer3 K3 - *1* , V3 [10,15,22] > >> > >> As you can see reducer1 has K3 - 1 and reducer3 has K3 - 1. > >> So is that case possible or every and every reducer has unique output > key? > >> > >> Thanks in advance > >> Oleg. > >> > >
