I was assuming binary format. 128-bits is a pretty heavy data type in many data models with measurable impact on performance versus using something smaller.
You also do not need 128-bits to decentralize unique key generation, even though it is quite reasonable if you design your keys well. Many do it with 64-bit unique keys in massive scale systems.
A subtle point that you may be overlooking is that while large-scale distributed databases, including all the ones I work on, export globally unique 128-bit keys, in most systems I’ve worked with they are internally represented and stored as 64-bits or less even if the key space is much larger than 64 bits. There are many different techniques for doing key space elision and inference that are used inside distributed databases to save space. The 128-bit value is only materialized when sending it over the wire to some external client system. But you don’t need to store it.
Literally storing a primary key in a distributed system as a 128-bit value is all downside with few benefits. For small systems the performance and scaling cost may not matter that much but in very large systems it matters a lot. It can — literally! — cost you millions of dollars per year.
You also do not need 128-bits to decentralize unique key generation, even though it is quite reasonable if you design your keys well. Many do it with 64-bit unique keys in massive scale systems.
A subtle point that you may be overlooking is that while large-scale distributed databases, including all the ones I work on, export globally unique 128-bit keys, in most systems I’ve worked with they are internally represented and stored as 64-bits or less even if the key space is much larger than 64 bits. There are many different techniques for doing key space elision and inference that are used inside distributed databases to save space. The 128-bit value is only materialized when sending it over the wire to some external client system. But you don’t need to store it.
Literally storing a primary key in a distributed system as a 128-bit value is all downside with few benefits. For small systems the performance and scaling cost may not matter that much but in very large systems it matters a lot. It can — literally! — cost you millions of dollars per year.