FB's MySQL team gave a tech talk on sharing circa 2011. A couple of bright engineers from Pinterest were there and asked a lot of great questions. A year or two later the same gentlemen presented their own MySQL infra at the Percona (?) conference. They'd used that talk as a springboard for their own design, which was quite clever and clearly integrated some of their unique business needs.
A decade later, I still remember how good their presentation was! I wish I could remember the engineers' names.