Re: An idle thought

On Thu, Mar 18, 2010 at 9:07 PM, Jeff Davis <pgsql@j-davis.com> wrote:
> The VM cause wrong results if a bit is set that's not supposed to be --
> right? Am I missing something? How does a seq scan skip visibility
> checks and still produce right results, if it doesn't rely on the bit?
>

There's also a PD_ALL_VISIBLE flag on the page header. We wal log when
we clear that bit so we can trust if it's set then all the tuples
really are visible. I forget whether we can trust it if it's *not* set
but there's not much point -- all tuples could become visible
spontaneously even the page is sitting on disk.
-- 
greg