RDB modules values serialization format version 2.
The original RDB serialization format was not parsable without the module loaded, becuase the structure was managed only by the module itself. Moreover RDB is a streaming protocol in the sense that it is both produce di an append-only fashion, and is also sometimes directly sent to the socket (in the case of diskless replication). The fact that modules values cannot be parsed without the relevant module loaded is a problem in many ways: RDB checking tools must have loaded modules even for doing things not involving the value at all, like splitting an RDB into N RDBs by key or alike, or just checking the RDB for sanity. In theory module values could be just a blob of data with a prefixed length in order for us to be able to skip it. However prefixing the values with a length would mean one of the following: 1. To be able to write some data at a previous offset. This breaks stremaing. 2. To bufferize values before outputting them. This breaks performance...
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