Cardinality & Capped Collections

#redis #capped-lists

참고 자료

Introduction to Capped Lists at redis.io

1. Cardinality of Collection¶

- LLEN key // List
- SCARD key // Set
- ZCARD key // Sorted-Set

2. Capped Collections¶

Retain subset of members

Use Cases

Leaderboard in a game
Recent Activity in Activity Stream

3. LTRIM¶

specify the range of elements you want to retain.
trimming can be specified from the left

> rpush list-one a b c d e f 
(integer) 6

> lrange list-one 0 -1 
1) "a" 
2) "b" 
3) "c" 
4) "d" 
5) "e" 
6) "f" 

> ltrim list-one 0 4 
"OK" 

> lrange list-one 0 -1 
1) "a" 
2) "b" 
3) "c" 
4) "d" 
5) "e"

4. ZREMRANGEBYRANK Key Start Stop - the Equivalent of LTRIM in Sorted Set¶

> ZADD set-one 1 a 2 b 3 c 4 d 5 e 6 f 
(integer) 6

> ZREMRANGEBYRANK set-one 5 -1 
(integer) 1

> zrange set-one 0 -1 
1) "a" 
2) "b" 
3) "c" 
4) "d" 
5) "e"

Last update: May 18, 2023
Created: May 16, 2023