Why is ruby build in pagination bad?

Eric Gross wrote:

Im trying to understand why the ruby pagination is slow and bad so that
I can write a good one of my own.

From my understanding, the ruby paginator, just takes the full results
set and display only the portion that you want it to display.

Nope, the built-in Rails paginator uses offset and limit to fetch only
the results for the current page.

According to this page:

http://glu.ttono.us/articles/2006/08/30/on-the-days-events

it's not the database-level stuff that's the problem, but the
view-level pagination helpers that have 'efficiency issues'. I haven't
been able to find a more detailed explanation, though.

Anyone care to enlighten us?

Chris