Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> Do we know in the optimizer whether we will be needing cheapest startup
> or not?
No. Higher levels might want either.
> Is the middle one kept because the optimizer has to mix the startup plus
> some percentage of the total cost for queries using LIMIT?
Right. There are potentially some ranges of LIMIT for which it could
win, I believe. Maybe with some math you could prove there is no range
in which the other two don't dominate it, but I suspect the extra logic
would slow down add_path more than it's worth.
regards, tom lane