hadoop2

I have few basic questions regarding HDFS Federation . Is it possible to read file created on one name node from another name node which is in the cluster federation? Does current version of Hadoop supports this feature? Ravindra babu Let me explain how Name node federation works as per Apache web site NameNode: In order to scale the name service horizontally, federation uses multiple independent Namenodes/namespaces. The Namenodes are federated; the Namenodes are independent and do not require coordination with each other. The Datanodes are used as common storage for blocks by all the

I have a silly doubt on Hadoop namenode memory calculation.It is mentioned in Hadoop book (Definite guide) as "Since the namenode holds filesystem metadata in memory, the limit to the number of files in a filesystem is governed by the amount of memory on the namenode. As a rule of thumb, each file, directory, and block takes about 150 bytes. So, for example, if you had one million files, each taking one block, you would need at least 300 MB of memory. While storing millions of files is feasible, billions is beyond the capability of current hardware." Since each taking one block, namenode

I am able to rename my reducer output file correctly but r-00000 is still persisting . I have used MultipleOutputs in my reducer class . Here is details of the that .Not sure what am i missing or what extra i have to do? public class MyReducer extends Reducer<NullWritable, Text, NullWritable, Text> { private Logger logger = Logger.getLogger(MyReducer.class); private MultipleOutputs<NullWritable, Text> multipleOutputs; String strName = ""; public void setup(Context context) { logger.info("Inside Reducer."); multipleOutputs = new MultipleOutputs<NullWritable, Text>(context); } @Override public