Hadoop / MapReduce is not a silver bullet

There are many problems that can be parallelized in MapReduce. But, it is not a silver bullet for every problem or algorithm.

Here is a list of things that it is not so good at solving (or When Not to MapReduce)
http://csci8980-2.blogspot.sg/2012/10/limitations-of-mapreduce-where-not-to.html

MapReduce is Good Enough?

If All You Have is a Hammer, Throw Away Everything That's Not a Nail!

http://www.umiacs.umd.edu/~jimmylin/publications/Lin_BigData2013.pdf‎