Using “varchar” as the primary key? bad idea? or ok?

Question

Is it really that bad to use \"varchar\" as the primary key?

(will be storing user documents, and yes it can exceed 2+ billion documents)

Answer 1

Use an ID (this will become handy if you want to show only 50 etc...). Than set a constraint UNIQUE on your varchar with the file-names (I assume, that is what you are storing).

This will do the trick and will increase speed.