| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Stephen Frost <sfrost(at)snowman(dot)net> |
| Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, Antonin Houska <ah(at)cybertec(dot)at>, Ants Aasma <ants(at)cybertec(dot)at>, Sasasu <i(at)sasa(dot)su>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: storing an explicit nonce |
| Date: | 2021-10-12 14:31:56 |
| Message-ID: | CA+TgmobKY7hUPMUTJdOUo2eThrkvVfHG4hxf1inH7RS7ZsBckg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Oct 11, 2021 at 1:30 PM Stephen Frost <sfrost(at)snowman(dot)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.
--
Robert Haas
EDB: http://www.enterprisedb.com
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