G1Joshi Apache Cassandra
Cassandra is a wide-column store database designed for scalability and high availability without compromising performance. Linear scalability and proven fault-tolerance on commodity hardware or cloud infrastructure make it the perfect platform for mission-critical data.
When to Use
- High Write Throughput: Ingests millions of writes per second.
- Always On: Zero single points of failure. Updates can happen even if nodes are down (Eventual Consistency).
- Multi-Region: Active-Active multi-region replication is built-in.
Quick Start (CQL)
CREATE TABLE users (
user_id UUID PRIMARY KEY,
name text,
email text
);
INSERT INTO users (user_id, name) VALUES (uuid(), 'Alice');
Core Concepts
Partition Key & Clustering Key
- Partition Key: Determines which node holds the data.
- Clustering Key: Sorts data within the partition on disk.
Tunable Consistency
You choose consistency level per query.
ANY: Fastest, least specific.QUORUM: Majority must acknowledge. Balanced.ALL: Slowest, safest.
Vector Search (5.0+)
Native support for Vector Search (ANN) allows using Cassandra as a Vector DB for AI apps.
Best Practices (2025)
Do:
- Query by Partition Key: Always. Scans are prohibited in production.
- Use SAI (Storage Attached Indexes): New in 5.0. Better than old secondary indexes.
- Denormalize: Optimize schema for Reads. It is okay to duplicate data into 3 tables to satisfy 3 different query patterns.
Don't:
- Don't use distributed joins: Cassandra doesn't do joins. Join in the app.
- Don't use large partitions: Keep partitions under 100MB to avoid compaction issues.