Introduction to Redis

1. What is Redis?

Redis (Remote Dictionary Server) is an in-memory key-value database.

Instead of storing data primarily on disk like PostgreSQL or MySQL, Redis keeps data in RAM, making it extremely fast (microseconds to milliseconds).

Example:

"user:1": {
  name: "Akkal",
  age: 22
}

You store data using a key and retrieve it later.

2. Why Redis?

Suppose your application fetches a user's profile from PostgreSQL.

Without Redis:

Client
   ↓
Backend
   ↓
PostgreSQL

Every request hits the database.

With Redis:

Client
   ↓
Backend
   ↓
Redis (cache)
   ↓ (miss)
PostgreSQL

If data exists in Redis (cache hit), response is returned immediately.
Otherwise (cache miss), data is fetched from PostgreSQL and stored in Redis for future requests.

This reduces:

Database load
Response time
Infrastructure costs

3. Installing Redis

Docker:

docker-compose.yml

services:
  redis:
    image: redis
    ports:
      - 6379:6379

docker compose up

Verify:

redis-cli ping

Output:

PONG

3.1 Create Redis Client

import Redis from "ioredis";
 
const client = new Redis("redis://127.0.0.1:6379");
 
client.on("error", (err) => console.log("Redis Client Error:", err));

4. Redis Basic Commands

4.1 SET & get

await client.set("name", "John Doe");

const value = await client.get("name");
console.log('Value for "name":', value);

Output:

Value for "name": John Doe

4.2 DELETE

const deleteCount = await client.del("name");
console.log("Deleted keys count:", deleteCount);

Output:

Deleted keys count: 1

4.3 MSET & MGET

await client.mset({
  "user:name": "Akkal Dhami",
  "user:age": "20",
  "user:country": "Nepal"
});

const [username, age, country] = await client.mget([
  "user:name",
  "user:age",
  "user:country"
]);
console.log(`Name: ${username}, Age: ${age}, Country: ${country}`);

Output:

Name: Akkal Dhami, Age: 20, Country: Nepal

4.4 LPUSH, RPUSH, LRANGE, LINDEX, LPOP, RPOP

await client.lpush("tasks", "Task 1");
await client.lpush("tasks", ["Task 2", "Task 3"]);
 
await client.rpush("tasks", "Task 4");

LPUSH inserts at the beginning.
RPUSH inserts at the end.

1. Get all elements

const tasks = await client.lrange("tasks", 0, -1);
console.log(tasks);

Output:

["Task 3", "Task 2", "Task 1", "Task 4"]

2. Get the first element

const task = await client.lindex("tasks", 0);
console.log(task);

Output:

Task 3

3. Get the last element

const task = await client.lindex("tasks", -1);
console.log(task);

Output:

Task 4

4. Get a range

First two items:

const task = await client.lrange("tasks", 0, 1);
console.log(task);

Output:

["Task 3", "Task 2"]

5. Remove and retrieve an item

From the left:

const task = await client.lpop("tasks");
console.log(task); // Task 3

From the right:

const task = await client.rpop("tasks");
console.log(task); // Task 4

4.5 SADD, SMEMBERS, SISMEMBER, SREM

Redis Set stores unique unordered values.

await client.sadd("fruits", "Apple");
await client.sadd("fruits", ["Banana", "Orange", "Mango"]);

After these operations, the set contains:

Apple
Banana
Orange
Mango

1. Get all members

const fruits = await client.smembers("fruits");
console.log("Fruits:", fruits);

Output:

Fruits: [ 'Apple', 'Banana', 'Orange', 'Mango' ]

Sets are unordered, so the order may vary.

2. Check if a value exists

const isMember = await client.sismember("fruits", "Banana");
console.log("Is Banana a member of fruits set?", isMember);

Output:

Is Banana a member of fruits set? 1

1 means the value exists.

0 means the value doesnot exist.

3. Remove an item

await client.srem("fruits", "Apple");

const updatedFruits = await client.smembers("fruits");
console.log("Updated Fruits:", updatedFruits);

Output:

Updated Fruits: [ 'Orange', 'Banana', 'Mango' ]

4.6 HSET, HGET

1. Creating a Hash

await client.hSet("user:1", {
  name: "Akkal",
  email: "akkal@example.com",
  age: "20",
});

2. Get all fields

const user = await client.hGetAll("user:1");
console.log(user);

Output:

{
  name: "Akkal",
  email: "akkal@example.com",
  age: "20"
}

3. Get a single field

const name = await client.hGet("user:1", "name");
console.log(name);

Output:

Akkal

4. Get multiple fields

const values = await client.hmGet(
  "user:1",
  ["name", "email"]
);
console.log(values);

Output:

[ 'Akkal', 'akkal@example.com' ]

5. Update a field

await client.hSet("user:1", "age", "23");

const user = await client.hGetAll("user:1");
console.log(user);

Output:

{
  name: "Akkal",
  email: "akkal@example.com",
  age: "23"
}

6. Check if a field exists

const exists = await client.hExists(
  "user:1",
  "email"
);
console.log(exists);

Output: 1

1 means the field exists.

7. Delete a field

await client.hDel("user:1", "age");

console.log(await client.hGetAll("user:1"));

Output:

{
  name: "Akkal",
  email: "akkal@example.com"
}

8. Count fields

const count = await client.hLen("user:1");
console.log(count);

Output: 2

9. Get only field names

const fields = await client.hKeys("user:1");
console.log(fields);

Output:

[ 'name', 'email' ]

10. Get only values

const values = await client.hVals("user:1");
console.log(values);

Output:

[ 'Akkal', 'akkal@example.com' ]