NoSQL

 NoSQL is a type of database management system (DBMS) that is designed to handle and store large volumes of unstructured and semi-structured data. Unlike traditional relational databases that use tables with pre-defined schemas to store data, NoSQL databases use flexible data models that can adapt to changes in data structures and are capable of scaling horizontally to handle growing amounts of data.

The term NoSQL originally referred to “non-SQL” or “non-relational” databases, but the term has since evolved to mean “not only SQL,” as NoSQL databases have expanded to include a wide range of different database architectures and data models.

NoSQL databases are generally classified into four main categories:

1. Document databases: These databases store data as semi-structured documents, such as JSON or XML, and can be queried using document-oriented query languages.
2. Key-value stores: These databases store data as key-value pairs, and are optimized for simple and fast read/write operations.
3. Column-family stores: These databases store data as column families, which are sets of columns that are treated as a single entity. They are optimized for fast and efficient querying of large amounts of data.
4. Graph databases: These databases store data as nodes and edges, and are designed to handle complex relationships between data.

Key Features of NoSQL:

1. Dynamic schema: NoSQL databases do not have a fixed schema and can accommodate changing data structures without the need for migrations or schema alterations.
2. Horizontal scalability: NoSQL databases are designed to scale out by adding more nodes to a database cluster, making them well-suited for handling large amounts of data and high levels of traffic.
3. Document-based: Some NoSQL databases, such as MongoDB, use a document-based data model, where data is stored in a schema-less semi-structured format, such as JSON or BSON.
4. Key-value-based: Other NoSQL databases, such as Redis, use a key-value data model, where data is stored as a collection of key-value pairs.
5. Column-based: Some NoSQL databases, such as Cassandra, use a column-based data model, where data is organized into columns instead of rows.
6. Distributed and high availability: NoSQL databases are often designed to be highly available and to automatically handle node failures and data replication across multiple nodes in a database cluster.
7. Flexibility: NoSQL databases allow developers to store and retrieve data in a flexible and dynamic manner, with support for multiple data types and changing data structures.
8. Performance: NoSQL databases are optimized for high performance and can handle a high volume of reads and writes, making them suitable for big data and real-time applications.

Types of NoSQL database: Types of NoSQL databases and the name of the database system that falls in that category are:

1. Graph Databases: Examples – Amazon Neptune, Neo4j
2. Key value store: Examples – Memcached, Redis, Coherence
3. Column: Examples – Hbase, Big Table, Accumulo
4. Document-based: Examples – MongoDB, CouchDB, Cloudant

When should NoSQL be used:

1. When a huge amount of data needs to be stored and retrieved.
2. The relationship between the data you store is not that important
3. The data changes over time and is not structured.
4. Support of Constraints and Joins is not required at the database level
5. The data is growing continuously and you need to scale the database regularly to handle the data.