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
