Redis persistent backup and recovery

Redis is a high-performance in-memory database whose advantages lie in fast data reading and high concurrency capabilities. However, since the data is all stored in memory, once the server crashes or goes down, the data will be lost. In order to avoid this situation, Redis provides a persistent storage function to write the data in the memory to the disk for data recovery when needed.

Redis has two persistence methods: RDB snapshot and AOF log. The implementation, advantages, disadvantages, and applicable scenarios of these two methods will be explained below.

1. RDB snapshot

RDB snapshot is a snapshot saving mechanism of Redis. It stores the data in Redis memory to the disk within a specified time interval and generates a RDB file. This file is a binary file that contains key-value pairs for all databases. When performing data recovery, you only need to load the file into Redis memory.

Advantages:

(1) It takes up little space, preserves data integrity, and saves disk space.

(2) The data recovery time is short, and it is faster to recover RDB files than to replay AOF logs.

Disadvantages:

(1) The data of the RDB file will only be saved once within the specified time interval. If Redis goes down during the regular saving time, data loss will occur.

(2) The real-time nature of data in RDB files is not high. If it is saved at too long an interval, it will cause data inconsistency problems for the business.

Applicable scenarios:

It is more suitable for business scenarios with large amounts of data and low reading and writing frequency, such as social applications, e-commerce applications, etc.

2. AOF log

AOF stands for Append-Only File, which is an append-only file. It is another persistence method of Redis. AOF log generates a log record for each operation based on Redis. When recovering data, you only need to perform these operations again.

Advantages:

(1) AOF can achieve almost no data loss. Even if abnormal situations such as downtime or power outage occur, the integrity of the data can be guaranteed as much as possible.

(2) AOF records each operation in real time, the data is highly real-time, and the log size and recording frequency can be controlled.

Disadvantages:

(1) AOF files are relatively large and may take up more disk space.

(2) AOF log files need to be rewritten from time to time, which will also cause performance burden.

Applicable scenarios:

Suitable for application scenarios that require high data integrity, such as the financial industry, pharmaceutical industry, etc.

3. Backup and Recovery

Redis provides two commonly used backup commands: BGSAVE and SAVE.

BGSAVE will save snapshots in the background and generate RDB files. It will not block the Redis read and write service. Therefore, it is easily exploited by centralized storms, causing the Redis service to be unavailable, so it needs to be used with caution.

SAVE will block all Redis requests while Redis is saving the snapshot and generating the RDB file. It will not continue to receive requests until the RDB file is generated successfully. In the case of large data volume or high memory usage, this command may cause the service to be blocked for a long time.

The way to restore data is also very simple. The RDB file is automatically read for recovery when Redis starts. If necessary, you can also manually execute the command to re-execute the AOF log to recover all data.

Summary:

How to choose the appropriate persistence method depends on the specific application scenario and business needs. If you have high requirements for data integrity, you can give priority to using the AOF log method; if the application is not sensitive to real-time data, you can use the RDB snapshot method, and you can also use the two persistence methods to achieve better recovery results. . At the same time, regular backup and recovery of data is also one of the important means to ensure data security.

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