I remember it well, because I was trying to explain why having tens of gigabytes of indexes wouldn't help them much if they only had 16Gb of RAM.
In terms of group-by performance, it depends a lot on the kind of data and how it's stored. For example, taking a sum on a columnar store is quite amenable to parallel solutions and a lot of databases will do that way.
I remember it well, because I was trying to explain why having tens of gigabytes of indexes wouldn't help them much if they only had 16Gb of RAM.
In terms of group-by performance, it depends a lot on the kind of data and how it's stored. For example, taking a sum on a columnar store is quite amenable to parallel solutions and a lot of databases will do that way.