Redis Basics: In-Memory Database Concepts, Data Structures, and Common Use Cases

1. Fundamentals

In-Memory Database

Redis is a key‑value store where each key maps to a single value, and all data resides in memory for high performance. The amount of data a single Redis instance can hold depends on the available RAM, and data can be persisted to disk to survive restarts.

Data Structures

Redis supports five native data structures:

String : the simplest type, storing up to 512 MB per key.

Hash : a collection of field‑value pairs, ideal for representing objects.

List : an ordered list of strings implemented as a doubly‑linked list, useful for feeds or message queues.

Set : an unordered collection of unique strings, supporting set operations such as intersection, union, and difference.

Zset (Sorted Set) : like a Set but each member has an associated score, enabling automatic ordering for leaderboards and ranking.

2. Common Redis Application Scenarios

Cache – Hot Data

Redis is often used to cache frequently read but rarely modified data, offering high QPS and durability options (AOF, RDB). When integrating with frameworks like Spring, developers typically check Redis before querying the database and invalidate the cache on updates, taking care to handle high‑concurrency edge cases.

Counters

Because Redis processes commands single‑threadedly, incrementing counters (e.g., page views) is atomic and millisecond‑level fast.

Queues

Redis lists can act as simple message queues or stacks, allowing sequential processing of concurrent requests and providing position information for ordering.

Bit Operations (Big Data Processing)

For billions‑scale datasets, Redis bitmaps (using SETBIT , GETBIT , BITCOUNT ) enable compact storage of flags such as user sign‑ins or online status, avoiding the memory explosion of one key per user.

Latest List

To serve a constantly updating feed (e.g., news), developers can push items onto a Redis list with LPUSH and fall back to a relational database to rebuild the list when memory is cleared.

Leaderboard

Sorted sets provide an efficient way to maintain ranking tables, automatically ordering members by score.

3. References

https://baijiahao.baidu.com/s?id=1636565352949240200

https://www.cnblogs.com/NiceCui/p/7794659.html