As long as you have a path that contains hdfs:/ you will not succeed as that is never going to be valid. In the comments you mentioned that you tried to add hdfs:// manually, which may be a nice hack, but in your code I don’t see you ‘clean up’ the wrong hdfs:/. So even … Read more
Humans can easily keep in mind about 7 entities +/- 2(wikipedia). When somebody needs to read the code they may run into this limit. Sometimes there are too many local variables to keep track of, or too many if/for statements. In all cases it makes it harder to understand what the code is supposed to … Read more
Almost any scientific code — finite differences, finite elements, etc. Which kind of leads to the circular answer, that any distributed program which doesn’t easily map to MapReduce would be better implemented with a more general MPI model. Not sure that’s much help to you, I’ll downvote this answer right after I post it.
What is UBER mode in Hadoop2? Normally mappers and reducers will run by ResourceManager (RM), RM will create separate container for mapper and reducer. Uber configuration, will allow to run mapper and reducers in the same process as the ApplicationMaster (AM). Uber jobs : Uber jobs are jobs that are executed within the MapReduce ApplicationMaster. … Read more
One problem with the Hadoop system is that by dividing the tasks across many nodes, it is possible for a few slow nodes to rate-limit the rest of the program. Tasks may be slow for various reasons, including hardware degradation, or software mis-configuration, but the causes may be hard to detect since the tasks still … Read more
There’s another thing to check when getting errors like this for classes which are writables, mappers, reducers, etc. If the class is an inner class, make sure it’s declared static (i.e. doesn’t need an instance of the enclosing class). Otherwise, Hadoop cannot instantiate your inner class and will give this same error – that a … Read more
In Map-Reduce for Machine Learning on Multicore Chu et al describe “algorithms that fit the Statistical Query model can be written in a certain “summation form,” which allows them to be easily parallelized on multicore computers.” They specifically implement 10 algorithms including e.g. weighted linear regression, k-Means, Naive Bayes, and SVM, using a map-reduce framework. … Read more
It’s not currently possible, but I would suggest voting for this case: https://jira.mongodb.org/browse/SERVER-2517.
Check out merge-sort. It turns out that sorting partially sorted lists is much more efficient in terms of operations and memory consumption than sorting the complete list. If the reducer gets 4 sorted lists it only needs to look for the smallest element of the 4 lists and pick that one. If the number of … Read more