The Redis cheat sheet

Quick reference

Keys

SCAN 0 MATCH user:* COUNT 100
EXISTS user:42
TYPE user:42
DEL user:42
UNLINK user:42

Strings

SET user:42:name Ada
GET user:42:name
SET lock:job 1 NX PX 30000
INCR page:views
MSET a 1 b 2

Hashes

HSET user:42 name Ada
HGET user:42 name
HGETALL user:42
HINCRBY user:42 logins 1
HDEL user:42 name
HSCAN user:42 0

Streams/TTL

XADD events * type signup
XLEN events
XREAD COUNT 10 STREAMS events 0
EXPIRE user:42 3600
TTL user:42
PERSIST user:42

Explained

Keys SCAN 0 MATCH user:* COUNT 100 walks the keyspace in slices instead of blocking on the whole thing. EXISTS user:42 answers whether a key is there, TYPE user:42 says what it is, DEL removes it synchronously, UNLINK removes it and frees memory in the background.

Strings SET user:42:name Ada stores a value, GET reads it, and SET lock:job 1 NX PX 30000 is the atomic lock: it only writes when the key is absent and expires after thirty seconds. INCR page:views is atomic, and MSET a 1 b 2 writes several keys in one round trip.

Hashes HSET user:42 name Ada sets a field, HGET reads one, HGETALL reads the whole hash, and HINCRBY user:42 logins 1 increments a counter without a read-modify-write race. HDEL removes a field, and HSCAN walks a large hash in slices.

Streams and TTL XADD events * type signup appends an entry with an auto ID, XLEN counts entries, and XREAD COUNT 10 STREAMS events 0 reads from the beginning. EXPIRE user:42 3600 sets a TTL, TTL reads it, and PERSIST removes it. TTL returns -1 for no expiry and -2 for a missing key.

In one line

Find the hot key

$redis-cli --bigkeys