On Wednesday, December 19, 2012, Robert Haas wrote:
On Wed, Dec 19, 2012 at 12:26 PM, Pavan Deolasee
<pavan.deolasee@gmail.com> wrote:
> I would like to run some pgbench tests where we get the system in a
> steady state such as all/most updates are HOT updates (not entirely
> unlikely scenario for many real life cases). And then try running some
> concurrent queries which can be executed via IOS. My gut feel is that,
> today we will see slow and continuous drop in performance for these
> queries because IOS will slowly stop working.
If there are no vacuums, I agree.
If the table is randomly updated over its entire size, then pretty much every block will be not-all-visible (and so disqualified from IOS) before you hit the default 20% vacuum threshold. I wonder if there ought not be another vac threshold, based on vm density rather than estimated obsolete tuple density.
Cheers,
Jeff