Although **Redis** is known as an **in-memory data store**, **persistence** allows **data** to be saved to **disk** to protect it from **loss** in case of **server crashes**. We'll explore the main **persistence methods** in Redis, their **configurations**, and **practical applications**.

# RDB Persistence

**RDB** (<u>Redis Database</u>) creates a full **snapshot** of Redis **data** at specific points in time. This method is suitable for scenarios where **speed** is important and occasional **data loss** is acceptable.

As shown in the **diagram**, **Redis** periodically creates **snapshots** of **data** and saves them to **disk**. This helps minimize **data loss** and simplifies restoring the **database state** during a **restart**.

The frequency of **snapshot creation** can be configured in the `redis.conf` file. 

To **view** and **modify** the `redis.conf` file on **macOS**:

To **view** the `redis.conf` file on **Windows**, you can open the **directory** where **Redis** is installed and access the `redis.windows.conf` file.


**After opening** the file, you'll see default **snapshot settings** like:

```
save 900 1      # save if at least 1 write operation occurred in the last 15 minutes.
save 300 10     # save if at least 10 write operations occurred in the last 5 minutes.
save 60 10000   # save if at least 10,000 write operations occurred in the last 1 minute.
```

In the example above, **Redis** will save **data** based on the following **criteria**:

- Every **900 seconds** (15 minutes) if at least **one key** was modified;
- Every **300 seconds** (5 minutes) if at least **10 keys** were modified;
- Every **60 seconds** if at least **10,000 keys** were modified.

The frequency of saving **data** to **disk** determines the level of **durability**. For example, if data is saved every **5 minutes**, and a **failure** occurs a few minutes after the last save, the data changes made during that period will be **lost**. Therefore, it's essential to carefully choose the **save interval**.

## How it Works
Redis saves the **database state** to an `.rdb` file at the specified intervals. When the **server** is restarted, the **data** is restored from the last saved file.

## Pros and Cons
RDB provides minimal impact on **performance** and uses a compact **storage format**. However, there is a risk of losing **data** added between **snapshot intervals**.

## Manual Snapshot Creation
Users can also trigger an RDB snapshot using the `SAVE` command. This command blocks the **Redis server**, so it should be avoided. Instead, the `BGSAVE` command should be used, as it creates a **child process** to take a snapshot in the **background**.

This course will introduce you to the fundamentals of Redis and its use in real-world applications. We'll cover key Redis commands, data types, key expiration and transactions, as well as how to integrate Redis with Spring for efficient data caching.

This section provides an introduction to Redis, highlighting its core features and common use cases. You’ll learn how to install Redis on different platforms, including Windows and macOS, and get familiar with the basics of connecting to and starting the Redis server.

Here, we explore the essential Redis commands for managing and manipulating data effectively. You'll learn how to set, retrieve, increment, and delete data using commands like SET, GET, EXISTS, INCR, DECR, and tackle practical tasks to apply these concepts in real-world scenarios.

Here, you will learn about key Redis data types, including Lists, Sets, Sorted Sets, and Hashes. You will explore their functionality and practical applications through focused exercises designed to reinforce your understanding of each data type.

You'll explore advanced features of Redis, including managing key lifecycles, executing transactions, and leveraging the Pub/Sub messaging system. Additionally, you'll learn essential security practices to safeguard your Redis environment against unauthorized access.

This section introduces the fundamentals of caching and demonstrates how to configure Redis as a cache in a Spring application. It covers key caching annotations and practical examples of caching queries in web applications, concluding with a summary of the main concepts.

Introduction to Redis

RDB Persistence

RDB Persistence

How it Works

Pros and Cons

Manual Snapshot Creation

1. What does the RDB method in Redis do?

2. What is an advantage of the RDB method?