Hadoop Certification Qusetions

Hadoop Certification Qusetions

1.When is the earliest point at which the reduce method of a given Reducer can be called?
A. As soon as at least one mapper has finished processing its input split.
B. As soon as a mapper has emitted at least one record.
C. Not until all mappers have finished processing all records.
D. It depends on the InputFormat used for the job.

Answer: C

HDFS client side mount table in hadoop2

HDFS client side mount table in hadoop2

HDFS federation it's possible to have multiple NameNode in a HDFS cluster. While this is good from a NameNode scalability and isolation perspective, it's difficult to manage multiple name spaces from a client application perspective. HDFS client mount table makes multiple names spaces transparent to the client. ViewFs more details on how to use the HDFS client mount table.

Earlier blog entry detailed how to setup HDFS federation. Let's assume the two NameNodes have been setup successfully on namenode1 and namenode2.