Runping Qi wrote:
When the reducers write the final results out, its output format is obtained
from the job object. By default, it is TextOutputFormat, and no conflicts.
However, if one wants to use SequencialFileFormat for the final results,
then the key/value classes are also obtained from the job object, the same
as the map tasks' output. Now we have a problem. It is impossible for the
map outputs and reducer outputs use different key/value classes, if one
wants the reducers generate outputs in SequentialFileFormat.
I have this problem in real situation. I solve it by creating my own output
format which is in fact copy-paste of the SequentialFileFormat with small
changes (simply a took output class from ohter (my own) job property). I
think
that each hadoop job shoud have posibility to denote output key/value from
reduce task (eg. {set,get}ReducerOutput{Key,Value}).
darek
