Re: Support UUIDv6 in uuid_extract_timestamp()

On Wed, Jun 24, 2026 at 4:29 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Wed, Jun 24, 2026 at 1:10 PM Tristan Partin <tristan(at)partin(dot)io> wrote:
> >
> > UUIDv6 is the same as UUIDv1 with some fields reordered. We already
> > supported UUIDv1, so let's add support for UUIDv6. Previously, calls to
> > uuid_extract_timestamp() would return NULL for UUIDv6 values.
> >
> > Patch 2 only adds comments. I think the bit manipulation is worthy of
> > comments, but others may disagree.
>
> Thank you for the patch!
>
> The patch seems reasonable to me. I'll review the patch in depth.
>

I've reviewed the v1 patches and the 0001 patch looks good to me. I
have one comment for the 0002 patch:

+ /*
+ * UUIDv1 splits the 60-bit Gregorian timestamp into three fields that
+ * are *not* stored most-significant-first (see RFC 9562 sec. 5.1):
+ *
+ * time_low (bits 0-31) octets 0-3, the least significant 32 bits
+ * time_mid (bits 32-47) octets 4-5, the middle 16 bits
+ * time_high (bits 48-59) octet 6 low nibble + octet 7, the most
+ * significant 12 bits (octet 6 high nibble
+ * holds the version and is masked off)
+ *
+ * Reassemble the timestamp by shifting each field back to its place.
+ */

pgindent destroys these field tables. We need to tell pgindent to
leave the block alone by adding the dashed comment form:

/*----------
* UUIDv6 is a field-compatible reordering of UUIDv1 that stores the
...
*----------
*/

Or I guess that this part doesn't necessarily need to be such a
format. Simply writing it like follow would work too:

/*
* UUIDv1 stores the 60-bit Gregorian timestamp in three fields that
* are *not* in most-significant-first order (RFC 9562 sec. 5.1):
* octets 0-3 hold the least significant 32 bits, octets 4-5 the
* middle 16, and octet 6's low nibble plus octet 7 the most
* significant 12. Octet 6's high nibble is the version, masked off
* below. The shifts put each field back in its place.
*/

Regards,

--
Masahiko Sawada
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