Hi
I have some questions and I would be really grateful to know the answer.
As I read in hadoop tutorial "the output files written by the Reducers are then
left in HDFS for user use, either by another
MapReduce job, a separate program, for human inspection."
1- Does hadoop automatically use the content of the files written by reducers?
I mean if 3 jobs are assigned to the hadoop, for example, and the 1st and 3rd
job are the same, does hadoop do the 3rd job again or automatically use the
results of first job? A more complicated Scenario is as follows:
A) 3 MapReduce jobs are assigned to hadoop
B) hadoop after doing 3 MapReduce jobs return the final result
C) in next step, 2 other jobs are assigned to hadoop. Both are repetitive
(hadoop have done them in step B)
Now, does hadoop automatically reuse the results of step A or do them again?
2-Are these files (files written by reducers) discarded? If so, when and how?
3- How hadoop users can know about the address of these files (files written by
reducers)?
Regards :-)
