Re: again on index usage

mlw <markw@mohawksoft.com> writes:
> ... Storage
> devices are now black boxes. The only predictable advantage a
> "sequential scan" can have on a modern computer is OS level caching.

You mean read-ahead.  True enough, but that "only advantage" is very
significant.  The 4.0 number did not come out of the air, it came
from actual measurements.

I think the real point in this thread is that measurements on an idle
system might not extrapolate very well to measurements on a heavily
loaded system.  I can see the point, but I don't really have time to
investigate it right now.  I'd be willing to reduce the default value of
random_page_cost to something around 2, if someone can come up with
experimental evidence justifying it ...

			regards, tom lane