This is great, thanks! It's great to have somewhere in the source to read about the optimizer! very cool!
> > > I suppose if the > > get_group_ids_of_current_user() function is marked as STABLE, would the > > optimizer cache this value for every row in a SELECT that returned > > multiple rows? > > While there was a patch to implement caching, it never finished. The > optimizer is allowed to, and sometimes does, choose plan shapes that reduce > the number of function calls. > So for multiple rows, it's possible that the same query could happen for each row? Even if it's clearly stable and only a read operation is happening? I suppose if the possibility exists that this could happen, perhaps using RLS for selects is not quite "production ready"? Or perhaps if the RLS qual/check is written well-enough, then maybe the performance hit wouldn't be noticed?
