Re: UUID v7

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: 2024-11-22 22:37:25
Message-ID: CAD21AoBWOnFu8kybJM7ah3P0g=qrByKF-k8tK=rTZEtc35=_JA@mail.gmail.com
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On Thu, Nov 21, 2024 at 1:22 PM Andrey M. Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
>
>
>
> > On 21 Nov 2024, at 02:24, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > But does replacing the least significant 2 bits
> > with random 2 bits really not affect monotonicity?
>
> You are right. We have to take into account this when calculating monotonicity. PFA another version.
>

While it works fine, I think we need a comment for this change:

-#define SUB_MILLISECOND_STEP ((NS_PER_MS / (1 << 12)) + 1)
+#if defined(__darwin__) || _MSC_VER
+#define SUB_MILLISECOND_BITS 10
+#else
+#define SUB_MILLISECOND_BITS 12
+#endif
+#define SUB_MILLISECOND_STEP ((NS_PER_MS / (1 << SUB_MILLISECOND_BITS)) + 1)

because the reader might think we should use SUB_MILLISECOND_BITS
here too at a glance:

+ /* sub-millisecond timestamp fraction (12 bits) */
+ increased_clock_precision = ((ns % NS_PER_MS) * (1 << 12)) / NS_PER_MS;

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com

In response to

  • Re: UUID v7 at 2024-11-21 21:22:10 from Andrey M. Borodin

Responses

  • Re: UUID v7 at 2024-11-23 07:58:09 from Masahiko Sawada

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