| From: | Jelte Fennema-Nio <postgres(at)jeltef(dot)nl> |
|---|---|
| To: | "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru> |
| Cc: | Sergey Prokhorenko <sergeyprokhorenko(at)yahoo(dot)com(dot)au>, pgsql-hackers mailing list <pgsql-hackers(at)postgresql(dot)org>, Aleksander Alekseev <aleksander(at)timescale(dot)com>, Przemysław Sztoch <przemyslaw(at)sztoch(dot)pl>, Nikolay Samokhvalov <nik(at)postgres(dot)ai>, "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Nick Babadzhanian <pgnickb(at)gmail(dot)com>, Mat Arye <mat(at)timescaledb(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Daniel Gustafsson <daniel(at)yesql(dot)se>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, Nikolay Samokhvalov <samokhvalov(at)gmail(dot)com>, "Kyzer Davis (kydavis)" <kydavis(at)cisco(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, "brad(at)peabody(dot)io" <brad(at)peabody(dot)io>, Kirk Wolak <wolakk(at)gmail(dot)com> |
| Subject: | Re: UUID v7 |
| Date: | 2024-01-29 20:38:27 |
| Message-ID: | CAGECzQTVi1JUE43uisQ+uKz46bQ+e+uwR9PUsmNfo2rjKaqwoA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, 29 Jan 2024 at 19:32, Andrey M. Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
> Even if the developer pass constant time to uuidv7(T) they will get what they asked for - unique identifier. Moreover - it still will be keeping locality. There will be no negative consequences at all.
It will be significantly "less unique" than if they wouldn't pass a
constant time. Basically it would become a UUIDv4, but with 74 bits of
random data instead of 122. That might not be enough anymore to
"guarantee" uniqueness. I guess that's why it is required to use
UUIDv8 in these cases, because correct usage is now a requirement for
assuming uniqueness. And for UUIDv8 the spec says this:
> UUIDv8's uniqueness will be implementation-specific and MUST NOT be assumed.
> > On 29 Jan 2024, at 18:58, Junwang Zhao <zhjwpku(at)gmail(dot)com> wrote:
> >
> > If other timestamp sources or
> > a custom timestamp epoch are required, UUIDv8 MUST be used.
>
> Well, yeah. RFC says this... in 4 capital letters :)
As an FYI, there is an RFC that defines these keywords that's why they
are capital letters: https://www.ietf.org/rfc/rfc2119.txt
> I believe it's kind of a big deficiency that k-way sortable identifiers are not implementable on top of UUIDv7. Well, let's go without this function. UUIDv7 is still an improvement over previous versions.
Yeah, I liked the feature to generate UUIDv7 based on timestamp too.
But following the spec seems more important than a nice feature to me.
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