How synchronization and backup are implemented
All supported versions of Valkey and Redis OSS support backup and synchronization between the primary and replica nodes. However, the way that backup and synchronization is implemented varies depending on the version.
Redis OSS Version 2.8.22 and Later
Redis OSS replication, in versions 2.8.22 and later, choose between two methods. For more information, see Redis OSS Versions Before 2.8.22 and Snapshot and restore.
During the forkless process, if the write loads are heavy, writes to the cluster are delayed to ensure that you don't accumulate too many changes and thus prevent a successful snapshot.
Redis OSS Versions Before 2.8.22
Redis OSS backup and synchronization in versions before 2.8.22 is a three-step process.
Fork, and in the background process, serialize the cluster data to disk. This creates a point-in-time snapshot.
In the foreground, accumulate a change log in the client output buffer.
Important
If the change log exceeds the client output buffer size, the backup or synchronization fails. For more information, see Ensuring you have enough memory to make a Valkey or Redis OSS snapshot.
Finally, transmit the cache data and then the change log to the replica node.
