Analysis of Redis persistence mechanism

Redis is a high-performance open source in-memory database, often used in scenarios such as caching, task queues, and message middleware. However, since Redis operates based on memory, abnormal situations such as power outages will cause data loss. Therefore, Redis provides two persistence mechanisms to ensure the security and reliability of data. Let’s analyze these two persistence mechanisms below. .

1. RDB persistence

RDB (redis database) is the default persistence method of Redis. When certain conditions are met, Redis will write the data snapshot in memory to the RDB file on disk. The format of the RDB file is binary and contains all key-value pair information of the database at the current point in time.

The advantages of RDB persistence are that it takes up little space and can restore data quickly because it only needs to load the RDB file into the memory.

There are two ways to trigger RDB persistence:

1) Manual operation

Execute the SAVE or BGSAVE command on the Redis client to manually trigger RDB persistence. The SAVE command will block the Redis server and will not return until the RDB file is written. BGSAVE allows the Redis server to perform RDB persistence operations in the background and will not block the normal service of the Redis server.

2) Automatic triggering

Configure the automatic triggering rules of Redis. When the rules are met, the RDB persistence operation will be automatically performed. It can be configured through the following settings in the redis.conf file:

save 900 1
save 300 10
save 60 10000

The settings here mean that when there are at least When 1 key-value pair changes, at least 10 key-value pairs change within 300 seconds, and at least 10,000 key-value pairs change within 60 seconds, the RDB persistence operation is triggered. Note that if multiple rules are set, Redis will perform RDB persistence operations in the order set.

2. AOF persistence

AOF (append only file) persistence is an append-based persistence mechanism. When Redis receives a command to modify the database, it will not only be executed, but also appended to the end of the AOF file.

The advantage of AOF persistence is that the data is more secure, because every operation to modify the database is recorded in AOF, ensuring minimal data loss, and the text format in the AOF file is easier to read and understand.

There are two ways to trigger AOF persistence:

1) Manual operation

Execute the BGREWRITEAOF command on the Redis client to manually trigger AOF persistence. This command will perform the rewriting operation of the AOF file in the background, re-record the commands executed by Redis into the new AOF file, and only retain the commands that affect the database.

2) Automatic triggering

You can set automatic triggering rules through the configuration in the redis.conf file. When the rules are met, the AOF file will be automatically rewritten:

auto- aof-rewrite-percentage 100
auto-aof-rewrite-min-size 64mb

The setting here indicates that when the size of the AOF file exceeds 64MB or the new AOF file size after AOF rewriting is the existing If the size of the AOF file is more than 100 times, the rewriting of the AOF file will be triggered.

In summary, RDB persistence and AOF persistence each have their own advantages and disadvantages, and should be selected and configured according to the actual situation. At the same time, it should be noted that while using the persistence mechanism, data backup and recovery testing should also be performed to ensure data security.

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