Redis vs Postgres

Comparisons · Reference cheat sheet

📋 Overview

Postgres is a durable relational system of record. Redis is an in-memory data structure server optimized for speed, caching, ephemeral state, and specialized structures. Often used together, not as mutual substitutes.

🔧 Core concepts

When to use Redis: cache, rate limits, sessions, leaderboards, pub/sub, queues (or Streams).

When to use Postgres: authoritative business data, complex queries, transactions, constraints.

💡 Examples

Redis cache aside:

GET user:42
# miss → load from Postgres → SET user:42 … EX 300

Postgres source of truth:

SELECT id, email FROM users WHERE id = 42;

⚠️ Pitfalls

• Using Redis as the only database without HA/persistence for critical data.
• Caching without invalidation strategy serves stale Postgres data forever.
• Storing huge blobs in Redis blows RAM — keep hot, small keys.

🔗 Related

• Redis/getting_started.md
• Postgres/getting_started.md
• Redis/expiry_ttl.md
• README.md