Re: timestamp with time zone ~> GMT

On Mon, Feb 3, 2025 at 12:23 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> =?utf-8?Q?=C3=81lvaro?= Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> > On 2025-Feb-03, Robert Treat wrote:
> >> This does seem to come up often enough that it probably is worth being
> >> a bit more explicit about how this works; attached patch attempts
> >> that.
>
> > LGTM.
>
> Hmm, I kind of like the up-front statement that timestamptz stores
> UTC. How about this simpler change?
>
> diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
> index 1d9127e94e..269809dc81 100644
> --- a/doc/src/sgml/datatype.sgml
> +++ b/doc/src/sgml/datatype.sgml
> @@ -2263,6 +2263,8 @@ TIMESTAMP WITH TIME ZONE '2004-10-19 10:23:54+02'
> then it is assumed to be in the time zone indicated by the system's
> <xref linkend="guc-timezone"/> parameter, and is converted to UTC using the
> offset for the <varname>timezone</varname> zone.
> + In either case, the originally stated or assumed time zone is not
> + retained.
> </para>

I thought the re-order made sense since the preceding paragraph talks
exclusively about behavior, so this paragraph first contrasts the
behavioral difference between the two, and then mentions the storage
aspects as part of that story.

I actually like the above as well, but if it were me I'd move all
mentions of storage (the existing + the above) to the end of the
paragraph after the behavior aspects.

> >> Note, I dropped the bit about GMT; that change was made ~40 years ago,
> >> and I suspect it is close to noise for many people these days, though
> >> it could be added back if folks feel strongly about it.
>
> > I don't feel strongly about it, but another option might be to add a
> > <footnote> so that it is still there but less intrusive. Grepping for
> > GMT in the postgres repo there are still over 1400 matches of all kinds.
>
> I think we'd better not remove the gloss for GMT just yet. It's still
> the magic boot value for the timezone GUC for example (cf pgtz.c),
> and it's still embedded in the IANA timezone database:
>
> $ ls /usr/share/zoneinfo/Etc
> GMT GMT+11 GMT+4 GMT+8 GMT-10 GMT-14 GMT-5 GMT-9 UTC
> GMT+0 GMT+12 GMT+5 GMT+9 GMT-11 GMT-2 GMT-6 GMT0 Universal
> GMT+1 GMT+2 GMT+6 GMT-0 GMT-12 GMT-3 GMT-7 Greenwich Zulu
> GMT+10 GMT+3 GMT+7 GMT-1 GMT-13 GMT-4 GMT-8 UCT
>
> Maybe we could move the info to the Glossary, but that seems like
> a separate matter from what's under discussion here.
>

Yeah, I think for end users this isn't compelling, but I figured there
might be some push back :-)

Robert Treat
https://xzilla.net