Redis

Redis

Redis (Remote Dictionary Server) is an in-memory data structure store, used as a database, cache, and message broker. It is incredibly fast.

When to Use

• Caching: The #1 use case. Cache HTML, JSON, or DB results.
• Session Store: User sessions (speed + automatic expiry).
• Queues: Simple background job queues using Lists (LPUSH/RPOP).
• Real-time: Leaderboards, Counting, Pub/Sub.

Quick Start

# Set a value with 10 second expiry
SET session:123 "active" EX 10

# Increment a counter atomically
INCR page:views

# Store a hash (object)
HSET user:100 name "Jeevan" role "admin"

Core Concepts

Single Threaded

Redis uses a main single thread. Requests are processed sequentially, atomic by design. (Though I/O threading runs in background).

Persistence (RDB vs AOF)

• RDB: Snapshots every X minutes. Fast restart, potential data loss.
• AOF: Logs every write. Slower, better durability.

Data Structures

Strings, Lists, Sets, Sorted Sets (ZSET), Hashes, Bitmaps, HyperLogLogs, Geospatial, Streams.

Best Practices (2025)

Do:

• Use Redis Stack: Includes extensions like RediSearch (FT.SEARCH), RedisJSON, and Bloom Filters.
• Use Connection Pooling: Opening connections is expensive.
• Set maxmemory-policy: Configure what happens when RAM is full (e.g., allkeys-lru to delete old data).

Don't:

• Don't use KEYS *: It blocks the server scanning all keys. Use SCAN.
• Don't store huge values: Redis is for small, fast data.

References

• Redis Documentation