Re: storing an explicit nonce

Greetings,

* Robert Haas (robertmhaas@gmail.com) wrote:
> On Mon, Oct 11, 2021 at 1:30 PM Stephen Frost <sfrost@snowman.net> wrote:
> > Regarding unlogged LSNs at least, I would think that we'd want to
> > actually use GetFakeLSNForUnloggedRel() instead of just having it zero'd
> > out.  The fixed value for GiST index pages is just during the index
> > build process, as I recall, and that's perhaps less of a concern.  Part
> > of the point of using XTS is to avoid the issue of the LSN not being
> > changed when hint bits are, or more generally not being unique in
> > various cases.
>
> I don't believe there's anything to prevent the fake-LSN counter from
> overtaking the real end-of-WAL, and if that should happen, then the
> buffer manager would get confused. Maybe that can be fixed by doing
> some sort of surgery on the buffer manager, but it doesn't seem to be
> a trivial or ignorable problem.

Using fake LSNs isn't new..  how is this not a concern already then?

Also wondering why the buffer manager would care about the LSN on pages
which are not BM_PERMANENT..?

I'll admit that I might certainly be missing something here.

Thanks,

Stephen