On 2013-05-31 13:14:13 -0400, Bruce Momjian wrote:
> On Thu, May 30, 2013 at 09:47:22AM -0400, Robert Haas wrote:
> > Well, as Heikki points out, I think that's unacceptably dangerous.
> > Loss or corruption of a single visibility map page means possible loss
> > of half a gigabyte of data.
> >
> > Also, if we go that route, looking at the visibility map is no longer
> > an optimization; it's essential for correctness. We can't decide to
> > skip it when it seems expensive, for example, as Jeff was proposing.
>
> Isn't the visibility map already required for proper return results as
> we use it for index-only scans. I think the optimization-only ship has
> sailed.
At the moment we can remove it without causing corruption. If we were to
use it for freezing we couldn't anymore. So there's a difference - how
big it is I am not sure.
Greetings,
Andres Freund
-- Andres Freund http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services