Caching Patterns

Redis as a Cache

Caching is Redis's most common use case. By storing frequently-accessed data in Redis, you avoid repeated expensive database queries or API calls.

Cache-Aside Pattern

The most common caching pattern:

1. Check Redis for the data
2. If found (cache hit), return it
3. If not found (cache miss), fetch from the database, store in Redis, return it

# Cache hit scenario:
SET cache:user:1 '{"name":"Alice","email":"a@b.com"}' EX 300
GET cache:user:1    -- returns cached JSON

# Cache miss scenario:
GET cache:user:99   -- (nil) → fetch from DB, then cache

SET with NX and XX Flags

SET key value NX — only set if key does not exist (like SETNX):

SET lock "worker-1" NX EX 30    -- acquire lock, expire in 30s
SET lock "worker-2" NX EX 30    -- fails if lock exists
GET lock                         -- "worker-1"

SET key value XX — only set if key exists (update only):

SET user:1 "Alice"
SET user:1 "Alice Updated" XX    -- updates existing key
SET user:99 "Bob" XX             -- (nil) — key doesn't exist

GETDEL — Get and Delete Atomically

Perfect for one-time use tokens:

SET otp:user123 "482910" EX 300
GETDEL otp:user123    -- "482910" (and deletes the key)
GETDEL otp:user123    -- (nil)

Distributed Lock Pattern

# Acquire: SET key value NX EX timeout
SET lock:resource "process-1" NX EX 30

# If successful ((integer) 1 returned or "OK"), we have the lock
# Do work...

# Release: delete the key (check it's still ours first!)
GET lock:resource    -- verify it's "process-1"
DEL lock:resource

Cache Warming

Pre-load frequently accessed data on startup:

MSET
  cache:config:maxitems "100"
  cache:config:timeout "30"
  cache:config:version "2"

Write-Through Cache

Update both the cache and database simultaneously:

SET user:1 "updated data" EX 3600
# Also write to database (in application code)

Your Task

Implement a simple lock using SET NX EX:

1. Set lock:task to "worker-1" with NX and EX 60 (acquires lock)
2. Try to set lock:task to "worker-2" with NX (should fail)
3. GET lock:task to confirm worker-1 holds the lock