It sounds like you are putting the byte string into a tuple and then packing that tuple to get the key-value pair that you store. Is that right? Is that because it is part of some larger data structure? If not, you could just put the bytes themselves into the value, with no further encoding at all. If so, then perhaps you need a different serialization format in place of tuples.
Tuples have nice ordering properties that make them a good choice for the key, but that aren’t needed for the value.
Thanks! That’s it. I realized that sometimes after posting this. Guess I originally thought I had to pack the record, as when fetching and returning that object is of type fdb.impl.value (iirc) which I didn’t handle correctly in my C program that used fdb via C Python bindings → fdb Python API.