Re: "68.4. Visibility Map" change suggestion.

On Mon, 2021-04-26 at 21:55 +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/12/storage-vm.html
> Description:
>
> Currently the documentation lists the line below;
>
> `Each heap relation has a Visibility Map (VM) to keep track of which pages
> contain only tuples that are known to be visible to all active
> transactions;`
>
> Should it instead read like;
>
> `Each heap relation has a Visibility Map (VM) to keep track of only those
> pages that contain tuples known to be visible to all active transactions;`
>
> After reading through the documentation and reading the first line, I first
> thought that VM only kept track of pages that only had visible tuples.
> Instead my understanding is that it shows which pages have any visible
> tuples in them.

I think that the wording of the documentation is more correct.

The VM also tracks the pages that are not all-visible. They have the
corresponding bit set to 0.

Yours,
Laurenz Albe