Horton

Re: UUID v7

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: "Andrey M. Borodin" <x4mmm@yandex-team.ru>
Cc: Sergey Prokhorenko <sergeyprokhorenko@yahoo.com.au>, Jelte Fennema-Nio <postgres@jeltef.nl>, Michael Paquier <michael@paquier.xyz>, Aleksander Alekseev <aleksander@timescale.com>, pgsql-hackers mailing list <pgsql-hackers@postgresql.org>, Peter Eisentraut <peter@eisentraut.org>, Przemysław Sztoch <przemyslaw@sztoch.pl>, "David G. Johnston" <david.g.johnston@gmail.com>, Mat Arye <mat@timescaledb.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Nikolay Samokhvalov <samokhvalov@gmail.com>, Junwang Zhao <zhjwpku@gmail.com>, Stepan Neretin <sncfmgg@gmail.com>
Date: 2024-11-19T19:06:35Z
Lists: pgsql-hackers

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On Tue, Nov 19, 2024 at 9:45 AM Andrey M. Borodin <x4mmm@yandex-team.ru> wrote:
>
>
>
> > On 19 Nov 2024, at 14:31, Andrey M. Borodin <x4mmm@yandex-team.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

Commits

  1. Fix timestamp overflow in UUIDv7 implementation.

  2. Add UUID version 7 generation function.

  3. Add some UUID support functions