Redis is a high-performance key-value database that supports a variety of data structures, such as strings, lists, sets, hashes, ordered sets, and more. An important feature of Redis is that it can persist data to disk to ensure data security and reliability. This article will introduce two persistence methods of Redis: RDB and AOF, as well as their advantages and disadvantages and update strategies.
The RDB (Redis Database) persistence method means that Redis writes the snapshot of the data set in the memory to the disk within a certain time interval, that is, Snapshotting. In this way, trigger conditions can be set through configuration files or commands, such as taking a snapshot every second or when the number of write operations is reached. RDB file is a file in binary format, which saves all the data of Redis at a certain point in time. When Redis restarts, it restores the data from the most recent RDB file.
The advantages of RDB persistence are:
- RDB files are compact and take up little space, making them suitable for backup and disaster recovery.
- RDB files can be easily transferred and migrated between different Redis servers.
- RDB persistence has little impact on the performance of Redis, because it is executed by the child process and will not block the main process.
The disadvantages of RDB persistence are:
- RDB persistence cannot achieve real-time or near-real-time data backup, because it is triggered periodically. If a failure occurs between two snapshots, the data during this period will be lost.
- During the snapshot process of RDB persistence, subprocesses need to be created, which may consume a large amount of memory and CPU resources, which will affect the service quality of Redis.
The AOF (Append Only File) persistence method means that Redis records every write operation into an append-only file, which is the AOF file. When Redis restarts, it replays all write operations from the AOF file, thereby restoring the data. AOF file is a file in plain text format, which saves all write commands executed by Redis.