> But is it? Is it impossible for the BRIN bitmap index scan to return 0 rows
> (say, if the value being matched is outside the min/max boundary for every
> block range?) Granted, if we document that it always returns 0 and should be
> ignored, then confusing the actual 0 with the 0 as a representation of
> “unknown” would be less a problem.
How about -1 ? It is an impossible value for sure. Maybe we should
change BitmapAnd and BitmapOr nodes, too. It is better to make it
obvious that it is not the correct value. I don't think many people
would notice the note on the documentation.
On the other hand, returning -1 broke parser of explain.depesz.com [1].
[1] http://explain.depesz.com/s/tAkd