The reason for not storing as a file on the operating system is that this is a Cache database.

Keeping multiple systems up-to-date with the same content would be better served via Mirroring rather than RSYNC. The more processes required to keep the whole system up-to-date, the greater the chances that Disaster Recovery requires more work than necessary. If server migration would be required, it is easer to copy one database file than many files.

However, and arguably more importantly, the idea that an object is a Stream that does not obviously allow different types of inherited instances (eg. Vehicles are a super of car, van and motorbike) seems 'under-achieving'.

It would be possible to have two properties, one BINARY and the other CHARACTER and populate according to the passed stream type but a getter would have to be added to decide which type has been stored and fetch appropriately.

Having it all done seamlessly with as few extra methods as possible gives a better approach (IMO).