# Redis Quick Reference

*Strings, lists, sets, hashes, pub/sub, persistence*

> Source: Redis Documentation (redis.io/docs) · MIT

## Connecting

### CLI

```
redis-cli
redis-cli -h 127.0.0.1 -p 6379
redis-cli -a password -n 2
redis-cli --tls -u rediss://user:pass@host:6380
```

### Driver Connection (Python)

```
import redis
r = redis.Redis(host='localhost', port=6379, db=0)
r.set('key', 'value')
print(r.get('key'))
```

### Server Info

```
PING           -- returns PONG
INFO server    -- server details
INFO memory    -- memory usage
DBSIZE         -- number of keys in current db
```

## Strings

### Basic Operations

```
SET name "Alice"
GET name
SET counter 100
MSET a 1 b 2 c 3
MGET a b c
```

### Numeric Operations

```
INCR counter        -- 101
INCRBY counter 10   -- 111
DECR counter        -- 110
DECRBY counter 5    -- 105
INCRBYFLOAT price 2.5
```

### String Commands

| Command | Description |
|---------|-------------|
| `SET key val` | Set string value |
| `GET key` | Get string value |
| `SETNX key val` | Set only if key does not exist |
| `SETEX key sec val` | Set with expiry in seconds |
| `APPEND key val` | Append to existing value |
| `STRLEN key` | Length of string value |

## Lists

### List Operations

```
LPUSH queue "first"
RPUSH queue "last"
LRANGE queue 0 -1    -- all elements
LPOP queue
RPOP queue
```

### List Commands

| Command | Description |
|---------|-------------|
| `LPUSH / RPUSH` | Push to left / right of list |
| `LPOP / RPOP` | Pop from left / right |
| `LRANGE key start stop` | Get range of elements |
| `LLEN key` | Length of list |
| `LINDEX key idx` | Element at index |
| `LREM key count val` | Remove count occurrences of val |
| `BLPOP key timeout` | Blocking pop (for queues) |

## Sets & Sorted Sets

### Set Operations

```
SADD tags "python" "redis" "docker"
SMEMBERS tags
SISMEMBER tags "python"   -- 1 (true)
SREM tags "docker"
SCARD tags                -- count
```

### Set Math

```
SUNION set1 set2       -- union
SINTER set1 set2       -- intersection
SDIFF set1 set2        -- difference
```

### Sorted Set Operations

```
ZADD leaderboard 100 "Alice" 85 "Bob"
ZRANGE leaderboard 0 -1 WITHSCORES
ZREVRANGE leaderboard 0 2
ZSCORE leaderboard "Alice"
ZRANK leaderboard "Alice"    -- 0-based rank
```

### Sorted Set Commands

| Command | Description |
|---------|-------------|
| `ZADD key score member` | Add member with score |
| `ZRANGE key start stop` | Range by rank (low to high) |
| `ZREVRANGE key start stop` | Range by rank (high to low) |
| `ZINCRBY key incr member` | Increment member score |
| `ZRANGEBYSCORE key min max` | Range by score value |
| `ZCARD key` | Number of members |

## Hashes

### Hash Operations

```
HSET user:1 name "Alice" age 30
HGET user:1 name
HGETALL user:1
HMSET user:2 name "Bob" age 25
HMGET user:1 name age
```

### Hash Commands

| Command | Description |
|---------|-------------|
| `HSET key field val` | Set hash field |
| `HGET key field` | Get hash field |
| `HGETALL key` | Get all fields and values |
| `HDEL key field` | Delete hash field |
| `HEXISTS key field` | Check field existence |
| `HINCRBY key field n` | Increment field value |
| `HKEYS key` | All field names |
| `HLEN key` | Number of fields |

## Keys & Expiry

### Key Commands

| Command | Description |
|---------|-------------|
| `KEYS pattern` | Find keys matching pattern (slow) |
| `SCAN cursor MATCH pat` | Iterate keys incrementally (safe) |
| `EXISTS key` | Check if key exists |
| `DEL key` | Delete key |
| `TYPE key` | Get key's data type |
| `RENAME key newkey` | Rename a key |

### Expiry Commands

```
EXPIRE key 3600       -- expire in 1 hour
PEXPIRE key 5000      -- expire in 5000 ms
TTL key               -- seconds until expiry
PTTL key              -- ms until expiry
PERSIST key           -- remove expiry
```

### Key Patterns

```
SET session:abc123 "data" EX 1800
-- EX = seconds, PX = milliseconds
-- NX = only if not exists
-- XX = only if exists
SET lock:order42 "owner" NX EX 10
```

## Pub/Sub

### Basic Pub/Sub

```
-- Subscriber (terminal 1)
SUBSCRIBE news alerts

-- Publisher (terminal 2)
PUBLISH news "Breaking: Redis 8 released"
```

### Pattern Subscribe

```
PSUBSCRIBE news.*
-- matches news.tech, news.sports, etc.
```

### Pub/Sub Commands

| Command | Description |
|---------|-------------|
| `SUBSCRIBE channel` | Listen for messages on channel |
| `PUBLISH channel msg` | Send message to channel |
| `PSUBSCRIBE pattern` | Subscribe to pattern |
| `UNSUBSCRIBE channel` | Stop listening |
| `PUBSUB CHANNELS` | List active channels |

## Transactions

### MULTI / EXEC

```
MULTI
SET balance:1 900
SET balance:2 1100
EXEC        -- executes atomically
```

### Optimistic Locking

```
WATCH balance:1
val = GET balance:1   -- read current
MULTI
SET balance:1 (val - 100)
EXEC
-- EXEC returns nil if balance:1 changed
```

### Transaction Commands

| Command | Description |
|---------|-------------|
| `MULTI` | Start transaction block |
| `EXEC` | Execute queued commands |
| `DISCARD` | Discard queued commands |
| `WATCH key` | Watch key for changes (optimistic lock) |
| `UNWATCH` | Forget all watched keys |

## Persistence

### RDB Snapshots

```
SAVE             -- synchronous snapshot
BGSAVE           -- background snapshot
LASTSAVE         -- timestamp of last save
```

### AOF (Append Only File)

| Command | Description |
|---------|-------------|
| `appendonly yes` | Enable AOF in redis.conf |
| `appendfsync always` | Fsync every write (safest, slowest) |
| `appendfsync everysec` | Fsync once per second (recommended) |
| `appendfsync no` | Let OS decide (fastest, riskiest) |

### Persistence Commands

```
CONFIG GET save
CONFIG SET save "900 1 300 10"
-- snapshot if 1 change in 900s or 10 in 300s
BGREWRITEAOF    -- rewrite AOF in background
```

## Common Patterns

### Distributed Lock

```
SET lock:resource "owner-id" NX EX 30
-- NX = acquire only if not held
-- EX 30 = auto-release after 30s
DEL lock:resource  -- explicit release
```

### Rate Limiter

```
key = "rate:user:42"
INCR key
EXPIRE key 60   -- 60-second window
-- reject if GET key > max_requests
```

### Caching Pattern

```
val = GET "cache:user:1"
if val is nil:
  val = fetch_from_db(1)
  SET "cache:user:1" val EX 300
```

### Session Storage

```
HSET sess:abc uid 42 role "admin"
EXPIRE sess:abc 1800   -- 30 min TTL
HGETALL sess:abc
```