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Redis supports a **set of core data structures**, each implemented as efficiently as possible for storage and manipulation in RAM.
These types are the foundation of everything Redis does.

### 1. String

The simplest, most basic data type, **key-value**.
It can store text, numbers, JSON, binary data, images, and more.

Example:

```bash
SET user:name "Alice"
GET user:name
```

Arithmetic is supported:

```bash
INCR counter
DECRBY counter 5
```

*A quirk:* a string in Redis can be up to **512 MB**.

### 2. List

An ordered collection of strings, like a queue or a stack.
Elements can be added and removed from either end.

Example:

```bash
LPUSH queue task1
RPUSH queue task2
LPOP queue
```

*Uses:* task queues, event feeds, chats.

### 3. Set

An unordered set of **unique** elements.
Supports set-theory operations: intersection, union, difference.

Example:

```bash
SADD tags "redis" "database" "cache"
SMEMBERS tags
SISMEMBER tags "redis"
```

*Uses:* storing unique IDs, subscribers, tags.

### 4. Sorted Set

Like `Set`, but every element has a **score**, a number that determines the sort order.

Example:

```bash
ZADD leaderboard 1500 "Alice" 1700 "Bob"
ZRANGE leaderboard 0 -1 WITHSCORES
```

*Uses:* rankings, leaderboards, prioritization, top lists.

### 5. Hash

Holds a set of *field-value* pairs under a single key.
It resembles a mini-object or JSON.

Example:

```bash
HSET user:100 name "Alice" age 25
HGET user:100 name
HGETALL user:100
```

*Uses:* user profiles, configuration, metadata.

### 6. Bitmap

Lets you store and manipulate individual bits of a string.

Example:

```bash
SETBIT users_online 100 1
GETBIT users_online 100
BITCOUNT users_online
```

*Uses:* activity tracking, online statistics, boolean flags.

### 7. HyperLogLog

A structure for the **approximate counting of unique elements** with minimal memory use (~12 KB).

Example:

```bash
PFADD visitors "user1" "user2" "user3"
PFCOUNT visitors
```

*Uses:* counting unique users, IPs, events.

### 8. Stream

A log of structured events (like Kafka).
Supports message IDs, consumer groups, acknowledgments.

Example:

```bash
XADD events * user "Alice" action "login"
XREADGROUP GROUP g1 c1 COUNT 1 STREAMS events >
```

*Uses:* task queues, events, microservices, logging.

### 9. Geo (geospatial data)

Lets you store coordinates and run geo-queries (finding nearby points, distances).

Example:

```bash
GEOADD shops 30.5 50.4 "ShopA"
GEORADIUS shops 30.5 50.4 10 km
```

*Uses:* maps, logistics, tracking, "near me" search.

### Summary

| Type | Purpose | Example use |
|---|---|---|
| String | Strings, numbers, JSON | Cache, tokens, counters |
| List | Ordered collections | Queues, feeds |
| Set | Unique elements | Subscriptions, tags |
| Sorted Set | Prioritized elements | Rankings, leaderboards |
| Hash | Objects, dictionaries | Profiles, configs |
| Bitmap | Bit-level flags | Online activity |
| HyperLogLog | Counting unique items | Analytics |
| Stream | Event streams | Queues, logging |
| Geo | Geo-coordinates | Distance search |

Redis isn't just a key-value store,
it's a **set of highly efficient in-memory data structures**
that can be combined for any scenario, from caching to streaming analytics.

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