I set rdbcompression lz4 on a Valkey 9.2.0-rc1 primary, watched a replica do a full sync, and measured exactly the same number of bytes going over the wire as with compression off. For a few minutes I believed the feature didn't touch replication at all. It does. I just had the wrong setting.

Valkey 9.2.0-rc1, released as a release candidate on 16 September with GA planned for mid-November, adds rdbcompression lz4 : whole-stream LZ4 compression for RDB files. Until now, RDB persistence has compressed each string value separately with LZF, a scheme the project's own issue tracker describes as "quite inefficient" because it can only find repetition inside one value, never across the file.…