ST_CONTAINS returns TRUE if geometry A contains geometry B. A contains B if and only if all points of B lie inside (i.e. in the interior or boundary of) A (or equivalently, no points of B lie in the exterior of A), and the interiors of A and B have at least one point in common. It is a predicate in postgis, but it is very slow.

I see H3 Uber has maxPolyfillSize but I cannot see an example as an alternative. Any ideas?

I know this is no code it is a very specific question, sorry in advance if that bothers.