Selection Criteria for Nosql Databases

A NoSQL (originally referring to "non SQL" or "non relational") database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relational databases. NoSQL databases are increasingly used in big data and real-time web applications. Some popular No-Sql databases include MongoDB, Redis, Couch DB, etc. But the question remains of how to select which No-Sql Databse for optimal performance based on your requirements?

To debunk the theory regarding it let’s look at the following points which acts as major factors while selecting No-SQL databases:

1. Storage Type

A good indicator towards making the right choice of NoSQL database is its storage type.

• For instance, get, put and delete functions are best supported by Key Value systems.
• Aggregation becomes much easier while using Column oriented systems as against the conventional row oriented databases. They use tables but do not have joins.
• Mapping data becomes easy from object oriented software using a Document oriented NoSQL database such as XML or JSON as they use structure document formats.

Concurrency control are what defines how two users can simultaneously edit the same bit of information. It happens quite often that one of the user is locked out and is unable to edit or perform other actions till the active user has finished editing. For instance:

• Locks prevent more than one active user to edit an entity such as a document, row or an object.
• MVCC (Multi-Version Concurrency Control), guarantee a read consistent view of the database, but result in conflicting versions of an entity if multiple users modify it at once. MVCC makes it possible for a transaction to seamlessly go through by maintaining many different versions of the object.

Replication ensures that mirror copies are always in sync.

• Synchronous Mode – Though it is an expensive approach as there is a dependency on the second server to respond, but it always ensures consistency. After receiving response from the second server, the first server sends back the ACK to the client. This ensures data is placed in multiple nodes at the same time.
• Asynchronous mode- In this mode, one database gets updated without waiting for the answer from the other database. Two databases could be not consistent in the range of few milliseconds.