Ask HN: How does Stripe manage IDs?

I like the way Stripe formats their IDs. It looks like they do identifier, underscore, random string (eg. cus_ja19382 for customers).

Does anyone know if they treat the ids as an opaque string or if they break it up and use the identifier portion too?

Wouldn’t it impact database performance if all your ids for a table start with “cus_”?