Hadoop

search-hadoop.com

search-hadoop.com indexes all the mailing lists and is great for historical searches. Search here first when you have an issue as its more than likely someone has already had your problem


 NoSQL

CAP Theorem

Good Article Explaining Eventual Consistency


 HBase

HBase Storage Architecture 

HBase vs BigTable 

HBase MapReduce Integration

HBase and HDFS Locality

HBase Coprocessors

HBase Real World Use Cases

Cassandra vs HBase


 Java

Java Interviews and Basic Concepts

Spark

Spark Gotchas

Spark Best Practices and Tuning Guide