Mastering Redis: When to Use Strings, Lists, Sets, Hashes, and Zsets

Redis is an open‑source in‑memory data structure store that can be used as a database, cache, and message broker.

It supports multiple data structures, built‑in replication, Lua scripting, LRU eviction, transactions, and various persistence levels. High availability is provided via Sentinel and Cluster automatic sharding.

Basic Data Types

String

Hash

List

Set

Sorted Set

Bitmap

HyperLogLog

Geospatial

String Details

1. Expiration time of a string is cleared when the value is reset.

127.0.0.1:6379> set hello 3
OK
127.0.0.1:6379> get hello
"3"
127.0.0.1:6379> ttl hello
(integer) -1
127.0.0.1:6379> expire hello 3000
(integer) 1
127.0.0.1:6379> set hello 4
OK
127.0.0.1:6379> ttl hello
(integer) -1

2. Setting a string value can overwrite keys of other types.

127.0.0.1:6379> sadd settest 1,2
(integer) 1
127.0.0.1:6379> type settest
set
127.0.0.1:6379> set settest hello
OK
127.0.0.1:6379> type settest
string
127.0.0.1:6379> sadd settest a,b
(error) WRONGTYPE Operation against a key holding the wrong kind of value

Application Scenarios

String

Cache data (e.g., activity titles, product info, configuration)

Simple counters (e.g., total participants of an event)

Timed expiration (e.g., daily sign‑in flag)

Distributed lock (e.g., SET lockkey 1 NX)

List

Queueing users (push/pop)

Ordered messages (push/pop)

Producer‑consumer model (push/pop, BRPOP/BLPOP for blocking reads)

Set

Deduplication lists

User tags, merchant tags

Set operations: intersection (common tasks), union (any task), difference (remaining tasks), random element (random gift)

Hash

Store multiple attributes of a single resource (e.g., user’s different gift counts)

Directly increment fields (e.g., HINCRBY giftA)

Sorted Set (Zset)

Leaderboards (user consumption, likes)

Key format: active:spring:star:rank → member=UserID, score=likes

Query top N, score range, or specific user score

Composite scoring using integer part for primary score and fractional part for secondary ranking

Best Practices

Assign reasonable TTL to every key.

String expiration is overwritten when the value is reset.

String SET can overwrite keys of other types; use appropriate data structures.

Plan key naming and quantity carefully; separate business domains (e.g., business Redis vs. activity Redis).

Leverage pipelines, Lua scripts, and transactions for performance.

Avoid using KEYS * on production clusters with many keys.

Do not store large volumes of data in a list and then search it.

Use a set to track user participation instead of creating a separate key per user.