Re: reducing random_page_cost from 4 to 2 to force index scan

On 2011-05-16 03:18, Greg Smith wrote:
> You can't do it in real-time. You don't necessarily want that to
> even if it were possible; too many possibilities for nasty feedback
> loops where you always favor using some marginal index that happens
> to be in memory, and therefore never page in things that would be
> faster once they're read. The only reasonable implementation that
> avoids completely unstable plans is to scan this data periodically
> and save some statistics on it--the way ANALYZE does--and then have
> that turn into a planner input.

Would that be feasible? Have process collecting the data every now-and-then
probably picking some conservative-average function and feeding
it into pg_stats for each index/relation?

To me it seems like a robust and fairly trivial way to to get better
numbers. The
fear is that the OS-cache is too much in flux to get any stable numbers out
of it.

--
Jesper