The term Big Data is an all-encompassing phrase that has various subdivisions addressing different needs of the customers. The most common description of Big Data talks about the four V’s: Volume, Velocity, Variety and Veracity.
Volume represents terabytes to exabytes of data, but this is data at rest. Velocity talks about streaming data requiring milliseconds to seconds of response time and is about data in motion. Variety is about data in many forms: structured, unstructured, text, spatial, and multimedia. Finally, veracity means data in doubt arising out of inconsistencies, incompleteness and ambiguities.
Hadoop is the first commercial version of Internet-scale supercomputing, akin to what HPC (high-performance computing) has done for the scientific community. It performs, and is affordable, at scale. No wonder it originated with companies operating at Internet scale, such as Yahoo in the 1990s, and then at Google, Facebook and Twitter.
In the scientific community, HPC was used for meteorology (weather simulation) and for solving engineering equations. Hadoop is used more for discovery and pattern matching. The underlying technology is similar: clustering, parallel processing and distributed file systems. Hadoop addresses the “volume” aspect of Big Data, mostly for offline analytics.
NoSQL products such as MongoDB address the “variety” aspect of Big Data: how to represent different data types efficiently with humongous read/write scalability and high availability for transactional systems operating in real time. The existing RDBMS solutions are inadequate to address this need with their schema rigidity and lack of scale-out solutions at low cost. Therefore, Hadoop and NoSQL are complementary in nature and do not compete at all.