Re: Proposal to add page headers to SLRU pages

> On Mar 9, 2024, at 05:22, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
>
> External Email
>
> On Wed, 2024-03-06 at 12:01 +0000, Li, Yong wrote:
>> Rebase the patch against the latest HEAD.
>
> The upgrade logic could use more comments explaining what's going on
> and why. As I understand it, it's a one-time conversion that needs to
> happen between 16 and 17. Is that right?
>
> Regards,
> Jeff Davis
>

> In the new code we effectively store only one LSN per page, which I
> understand is strictly worse. Maybe the idea of doing away with these
> LSN groups should be reconsidered ... unless I completely misunderstand
> the whole thing.
>
> --
> Álvaro Herrera PostgreSQL Developer —

Thanks for the comments on LSN groups and pg_upgrade.

I have updated the patch to address both comments:
- The clog LSN group has been brought back.
Now the page LSN on each clog page is used for honoring the write-ahead rule
and it is always the highest LSN of all the LSN groups on the page.
The LSN groups are used by TransactionIdGetStatus() as before.
- New comments have been added to pg_upgrade to mention the SLRU
page header change as the reason for upgrading clog files.

Regards,
Yong