[netcraft]

we use both uuid's created in our application layer and stored as char(35) and also uuid's produced in the database stored as uuid data types. We have tens of millions of records and have no issues. Once we get upgraded to PG10 and can use hash indexes for them we expect a further speedup.

I don't know anything about the author, but every time in the past ive heard someone say that uuid's as keys are a problem it turns out theyve never actually tried it, theyre just saying what theyve heard in the past. Theoretically they should be worse than they are - and theres no doubt that a regular int/bigint would be faster - but the truth is there are so many other things that are going to slow you down before that.