What is the difference between Cassandra and PostgreSQL? Please describe the main differences.

Cassandra and PostgreSQL are two different database management systems, oriented towards different tasks and architectures.

• Database type:

  • Cassandra is a distributed NoSQL database focused on storing large volumes of data with high availability and scalability.
  • PostgreSQL is a relational DBMS supporting ACID, complex queries, and transactions.

• Data model:

  • Cassandra uses a wide-column store model, where data is stored in tables with dynamic columns.
  • PostgreSQL uses a relational model with tables, rows, and columns, supporting complex relationships and normalization.

• Scalability:

  • Cassandra is designed for horizontal scaling and operates in a cluster with many nodes.
  • PostgreSQL traditionally scales vertically, although there are solutions for sharding and replication.

• Transactions and consistency:

  • PostgreSQL supports full transactions with strong consistency.
  • Cassandra is oriented towards eventual consistency, with configurable levels of consistency.

• Query language:

  • PostgreSQL uses SQL with extensions.
  • Cassandra uses CQL (Cassandra Query Language), similar to SQL but with limitations.

• Usage:

  • Cassandra is suitable for systems with huge data volumes, where high availability and scalability are crucial.
  • PostgreSQL is suitable for systems requiring complex queries, transactions, and strict consistency.

Example: if you need a database for analytics with a huge data flow and fault tolerance, choose Cassandra. If you need a classic relational database with transactions — PostgreSQL.