Ken Tanzer <ken(dot)tanzer(at)gmail(dot)com> writes:
> Hi. I'm wondering if this is normal or at least known behavior?
> Basically, if I'm specifying a LIMIT and also NULLS FIRST (or NULLS LAST
> with a descending sort), I get a sequence scan and a couple of orders of
> magnitude slower query. Perhaps not relevantly, but definitely ironically,
> the sort field in question is defined to be NOT NULL.
The index won't get credit for matching the requested ordering if it's
got the wrong null-ordering polarity. There's not an exception for
NOT NULL columns. If you know the column hasn't got nulls, why are
you bothering with a nondefault null-ordering request?
regards, tom lane