Horton

Re: UUID v7

Peter Eisentraut <peter@eisentraut.org>

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From: Peter Eisentraut <peter@eisentraut.org>
To: "Andrey M. Borodin" <x4mmm@yandex-team.ru>
Cc: Aleksander Alekseev <aleksander@timescale.com>, pgsql-hackers mailing list <pgsql-hackers@postgresql.org>, Sergey Prokhorenko <sergeyprokhorenko@yahoo.com.au>, Jelte Fennema-Nio <postgres@jeltef.nl>, 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>
Date: 2024-04-04T13:45:21Z
Lists: pgsql-hackers 
On 26.03.24 18:26, Andrey M. Borodin wrote:
>> Also, you are initializing 4 bits (I think?) to zero to guard against counter rollovers (so it's really just an 8 bit counter?).  But nothing checks against such rollovers, so I don't understand the use of that.
> No, there's only one guard rollover bit.
> Here: uuid->data[6] = (uuid->data[6] & 0xf7);
> Bits that are called "guard bits" do not guard anything, they just ensure counter capacity when it is initialized.

Uh, I guess I don't understand this at all.  I tried to dig up some 
information about this, but didn't find anything.  What exactly is the 
mechanism of these "counter rollover guards"?  If they don't guard 
anything, what are they supposed to accomplish?

Commits

  1. Fix timestamp overflow in UUIDv7 implementation.

  2. Add UUID version 7 generation function.

  3. Add some UUID support functions