On Mar 16, 2011, at 7:44 PM, Robert Haas wrote:
> It
> would be really nice (for this and for other things) if we had some
> way of measuring the I/O saturation of the system, so that we could
> automatically adjust the aggressiveness of background processes
> accordingly.
Has anyone looked at the overhead of measuring how long IO requests to the kernel take? If we did that not only could
weget an idea of what our IO workload looked like, we could also figure out whether a block came out of cache or not.
Thatinformation could potentially be useful to the planner, but even if the database couldn't use that knowledge itself
itwould be a damn useful statistic to have... IMHO, far more useful than our current hit rate statistics.
--
Jim C. Nasby, Database Architect jim@nasby.net
512.569.9461 (cell) http://jim.nasby.net