I use UUIDs in mysql as primary keys in tables with a few million records, and I'm about to migrate a few tables with billions of records from bigint to uuid.
Never saw any real problem. I use char(36), as it's easier to query manually when needed, but I' looking into binary(16) for those billion row tables.
I think most issues with fragmented tables are old problems since ssd, and the overhead is something you will only notice in benchmarks.
If your keys ate supposed to be uuids, the just use them and get the hardware to handle it. In reality, you're most likely to be affected by a zillion other things before an uuid as pk.
Never saw any real problem. I use char(36), as it's easier to query manually when needed, but I' looking into binary(16) for those billion row tables.
I think most issues with fragmented tables are old problems since ssd, and the overhead is something you will only notice in benchmarks.
If your keys ate supposed to be uuids, the just use them and get the hardware to handle it. In reality, you're most likely to be affected by a zillion other things before an uuid as pk.