Redis Cheatsheet

Key Concepts

• a in-memory key-value store, store and retrieve using a unique key
• can be used as a database, cache, and/or messsage broker
• supports numbers, strings, hashes, lists, sets, sorted sets

why is it so fast?

• Redis keeps everything in RAM

How does it manage data?

• data expirations (set expiration times for keys)
• data partitioning (divide large datasets into smaller, more manageable chunks)
• offloading to persistent storage (store less frequently accessed data on disk, snapshots or log files)
• clustering (distribute across multiple redis instances)

what happens if data in memory grows beyond the configured memory limit?

• data eviction
  • volatile-lru: evicts the LRU key from among the keys with an expiration set
  • allkeys-lru: evicts the LRU key from all keys
  • volatile-ttl: evicts the key with the nearest expiration time
  • allkeys-random: evicts a random key from all keys
  • volatile-random: evicts a random key from among the keys with an expiration set
  • noeviction: error when memory limit is reached
• Disk Persistence
  • RDB (Redis Database Backup): snapshot-based persistence method. configure to take period snapshots and save them to disk in binary format
  • AOF (append-only file): this log is written to disk, allow redis to replay the log
    • can be configured to save after every command, every second, or at specific times
  • No Persistence
  • RDB and AOF can be configure to work together

In case of hardware failure or server restarts, what happens?

• Redis can load data back into memory from disk (from most recent snapshots or append-only-files)