Redis Cheat Sheet

Transaction Example (Optimistic Locking)

WATCH mykey
val = GET mykey
val = val + 1
MULTI
SET mykey $val
EXEC
# EXEC returns nil if mykey was modified by another client

Lua Script Example (Atomic Compare-and-Set)

# Atomic compare-and-set: only update if current value matches
EVAL "
  if redis.call('GET', KEYS[1]) == ARGV[1] then
    return redis.call('SET', KEYS[1], ARGV[2])
  else
    return nil
  end
" 1 mykey "old_value" "new_value"

Persistence Options Comparison

Caching Pattern (Cache-Aside)

Check cache first. On miss, load from database and store in cache with a TTL to prevent stale data.

# Pseudocode for cache-aside pattern
value = GET "cache:user:123"
if value is nil:
    value = db.query("SELECT * FROM users WHERE id=123")
    SET "cache:user:123" value EX 300    # Cache for 5 minutes
return value

# Invalidate on update
DEL "cache:user:123"

Rate Limiting (Sliding Window)

Limit API calls per user using a sorted set with timestamps. Clean up expired entries on each check.

# Allow 100 requests per 60 seconds per user
MULTI
ZREMRANGEBYSCORE "ratelimit:user:42" 0 (NOW - 60)
ZADD "ratelimit:user:42" NOW NOW
ZCARD "ratelimit:user:42"
EXPIRE "ratelimit:user:42" 60
EXEC
# If ZCARD result > 100, reject the request

Rate Limiting (Fixed Window Counter)

Simple counter-based rate limiting. Lighter than the sliding window but less precise at boundaries.

# Allow 100 requests per minute
key = "ratelimit:user:42:" + current_minute
count = INCR key
if count == 1:
    EXPIRE key 60
if count > 100:
    reject request

Session Management

Store user sessions as Redis hashes with automatic expiry. Fast reads/writes for session data.

# Create session
HSET "session:abc123" user_id 42 role "admin" created_at 1707667200
EXPIRE "session:abc123" 3600       # 1 hour TTL

# Read session
HGETALL "session:abc123"

# Refresh session TTL on activity
EXPIRE "session:abc123" 3600

# Destroy session (logout)
DEL "session:abc123"

Distributed Lock (Redlock Pattern)

Use SET NX with an expiry to implement a simple distributed lock. Always include a unique token for safe release.

# Acquire lock (only if not held)
SET "lock:resource" "unique-token-abc" NX EX 30

# Release lock (only if we hold it) — use Lua for atomicity
EVAL "
  if redis.call('GET', KEYS[1]) == ARGV[1] then
    return redis.call('DEL', KEYS[1])
  else
    return 0
  end
" 1 "lock:resource" "unique-token-abc"

Leaderboard

Use sorted sets for real-time leaderboards with O(log N) inserts and O(log N + M) range queries.

# Add or update a player's score
ZADD "leaderboard:game1" 1500 "player:42"

# Get top 10 players
ZREVRANGE "leaderboard:game1" 0 9 WITHSCORES

# Get a player's rank (0-indexed, highest first)
ZREVRANK "leaderboard:game1" "player:42"

# Increment a player's score
ZINCRBY "leaderboard:game1" 50 "player:42"