Re: Idea for getting rid of VACUUM FREEZE on cold pages

On Fri, 2010-06-04 at 10:18 -0400, Tom Lane wrote:
> Jan Wieck <JanWieck(at)Yahoo(dot)com> writes:
> > On 6/2/2010 3:10 PM, Alvaro Herrera wrote:
> >> I'd prefer a setting that would tell the system to freeze all tuples
> >> that fall within a safety range whenever any tuple in the page is frozen
> >> -- weren't you working on a patch to do this? (was it Jeff Davis?)
>
> > I just see a lot of cost caused by this "safety range". I yet have to
> > see its real value, other than "feel good".
>
> Jan, you don't know what you're talking about. I have repeatedly had
> cases where being able to look at xmin was critical to understanding
> a bug. I *will not* hold still for a solution that effectively reduces
> min_freeze_age to zero.

Recent history shows Tom's view to be the most useful one: its useful to
keep seeing the xmin. The last time we altered the way we set hint bits
we caused multiple data loss bugs doing it. We will need to debug things
and the WAL is always long gone (great idea though).

Why not just have a separate flag for HEAP_XMIN_FROZEN, that way we can
keep the xmin but also can see it is frozen?

We already WAL-log certain flag settings, so why not this one also?

--
Simon Riggs www.2ndQuadrant.com