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NoSQL

NoSQL is the umbrella term for non-relational databases, including document, key-value, column-family, and graph models, designed for scalability and flexible schemas.

Purpose

To address relational database limitations in massive data volumes, flexible schemas, and horizontal scaling.

Mechanism

Four major types: document (MongoDB, JSON documents), key-value (Redis, simple and fast), column-family (Cassandra, wide sparse rows), graph (Neo4j, relationship-dense). Trades part of ACID for BASE eventual consistency and horizontal scaling. No fixed schema (or flexible schema).

Use cases

  • Horizontal scaling of massive data
  • Flexible/dynamic schemas
  • Caching and session storage
  • Social graphs and recommendations

Examples

  • Input 
    db.users.insert({name:"Ada",tags:[...]})
    Output 
    No fixed schema

    Document store

Common errors

Assuming NoSQL needs no data modeling
Document structure and indexes still need design

Related terms

SQL
SQL (Structured Query Language) is the standard query language of relational databases, defining and manipulating data declaratively (DDL/DML/DQL/DCL).
GLOSSARY
ACID
ACID is the four properties of relational transactions: atomicity (all or nothing), consistency (constraints preserved), isolation (concurrency without interference), and durability (committed data is never lost).
GLOSSARY
BASE
BASE is the weak-consistency NoSQL model: basically available, soft state, eventually consistent — trading strong consistency for availability and scalability.
GLOSSARY
CAP Theorem
The CAP theorem states that under network partition a distributed system can satisfy only one of consistency (C) or availability (A); all three cannot hold at once.
GLOSSARY

References