Hadoop ecosystem questions

Pig
UDF
Map Reduce
When you do join in Hive, what's going on behind the scene.
Redis

1. What is Kafka:
    Scala based distributed messaging system .

2. What is Cassandra:
    A distributed NOSQL database(Key-Value Document-based), it doesn't support MapReduce

3. What is Redis:
    In memory data structure store. Let's say you have 400TB data and you want to access them very fast
    in a local variable. you want to use Redis.

news source

https://www.bloomberg.com/markets
http://www.cnbc.com/investing/
http://www.reuters.com/news/archive/marketsNews?view=page&page=1&pageSize=100
http://www.marketwatch.com/
https://www.google.com/finance/market_news?ei=QDonWfmzNc6amAHqpLGQDQ