Re: UUID v7

> On 19 Mar 2024, at 13:55, Peter Eisentraut <peter@eisentraut.org> wrote:
> 
> On 16.03.24 18:43, Andrey M. Borodin wrote:
>>> On 15 Mar 2024, at 14:47, Aleksander Alekseev <aleksander@timescale.com> wrote:
>>> 
>>> +1 to the idea. I doubt that anyone will miss it.
>> PFA v22.
>> Changes:
>> 1. Squashed all editorialisation by Jelte
>> 2. Fixed my erroneous comments on using Method 2 (we are using method 1 instead)
>> 3. Remove all traces of uuid_extract_variant()
> 
> I have committed a subset of this for now, namely the additions of uuid_extract_timestamp() and uuid_extract_version().  These seemed mature and agreed upon.  You can rebase the rest of your patch on top of that.

Great! Thank you! PFA v23 with rebase on HEAD.

> I have started a separate discussion to learn about the precision we can expect from gettimeofday().

Even in presence of real microsecond-enabled and portable timer using microseconds does not seem to me an optimal way of utilising UUID bits.

Timer-based bits contribute to global sortability. But the real timers we have are not even millisecond adjusted. We can hope for ~few ms variation in one datacenter or in presence of atomic clocks.

Time-based bits contribute to global uniqueness, but certainly they are not that effective as counter bits.

Time-based bits do not provide local sortability guarantees: some UUIDs might get same microseconds or be affected by leap backwards.

I think that microseconds are good only for hardware-specific solutions, not for something that runs on variety of platforms, OSes, devices.


Best regards, Andrey Borodin.