| From: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> |
|---|---|
| To: | "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru> |
| Cc: | Sergey Prokhorenko <sergeyprokhorenko(at)yahoo(dot)com(dot)au>, Jelte Fennema-Nio <postgres(at)jeltef(dot)nl>, Michael Paquier <michael(at)paquier(dot)xyz>, Aleksander Alekseev <aleksander(at)timescale(dot)com>, pgsql-hackers mailing list <pgsql-hackers(at)postgresql(dot)org>, Peter Eisentraut <peter(at)eisentraut(dot)org>, Przemysław Sztoch <przemyslaw(at)sztoch(dot)pl>, "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Mat Arye <mat(at)timescaledb(dot)com>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, Nikolay Samokhvalov <samokhvalov(at)gmail(dot)com>, Junwang Zhao <zhjwpku(at)gmail(dot)com>, Stepan Neretin <sncfmgg(at)gmail(dot)com> |
| Subject: | Re: UUID v7 |
| Date: | 2024-11-19 19:06:35 |
| Message-ID: | CAD21AoBTPXU5s6WZyANZdwdvfRNjUHjFxWD1xnvUG9gJeQDfGg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Nov 19, 2024 at 9:45 AM Andrey M. Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
>
>
>
> > On 19 Nov 2024, at 14:31, Andrey M. Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
> >
> > Done.
>
> Here's v33 intact + one more patch to add 2 bits of entropy on MacOS (to compensate lack of nanoseconds).
> What do you think?
>
Thank you for updating the patch!
I've reviewed the v33 patch and made some changes mostly for cosmetic
things. Please review it to see if we accept these changes.
I have one question about the additional patch:
+#if defined(__darwin__)
+ /*
+ * On MacOS real time is truncted to microseconds. Thus, 2 least
+ * significant bits of increased_clock_precision are neither random
+ * (CSPRNG), nor time-dependent (in a sense - truly random). These 2 bits
+ * are dependent on other time-specific bits, thus they do not contribute
+ * to uniqueness. To make these bit random we mix in two bits from CSPRNG.
+ */
+ uuid->data[7] = uuid->data[7] ^ (uuid->data[8] >> 6);
+#endif
I thought that the whole 12 bits in "rand_a" is actually
time-dependent since we store 1/4096 fraction of sub-milliseconds. Am
I missing something?
Regards,
--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com
| Attachment | Content-Type | Size |
|---|---|---|
| change_v33.patch | application/octet-stream | 12.6 KB |
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