Memory-comparable Serialization of Data Types

We are currently integrating LSM-tree based storage engine RocksDB into Postgres. I am wondering is there any function that serialize data types in memory-comparable format, similar to MySQL and MariaDB. With that kind of function, we can directly store the serialized format in the storage engine and compare them in the storage engine level instead of deserializing data and comparing in the upper level. I know PostgreSQL is towards supporting pluggble storage engine, so I think this feature would be particular useful.

Best,

Shichao