By any chance, were you thinking of the Database Care and Feeding guide? That was a PDF doc we often circulated to address performance issues, but that was back in the 4.7.x days. That guide is no longer applicable, especially given performance improvements built in to 5.0 forward; instead, if you run into any specific performance problems, we usually address those on a case-by-case basis through Support.
Not sure if that's what you had in mind though, just going on a hunch since that was my go-to guide for a while.