On 17 November 2015 at 15:43, Jim Nasby <Jim.Nasby@bluetreble.com> wrote:
> On 11/17/15 4:41 AM, Thom Brown wrote:
>>
>> Could someone post a TL;DR summary of what the current plan looks
>> like? I can see there is a huge amount of discussion to trawl back
>> through. I can see it's something to do with the visibility map. And
>> does it avoid freezing very large tables like the title originally
>> sought?
>
>
> Basically, it follows the same pattern that all-visible bits do, except
> instead of indicating a page is all-visible, the bit shows that all tuples
> on the page are frozen. That allows a scan_all vacuum to skip those pages.
So the visibility map is being repurposed? And if a row on a frozen
page is modified, what happens to the visibility of all other rows on
that page, as the bit will be set back to 0? I think I'm missing a
critical part of this functionality.
Thom
