| From: | Noah Misch <noah(at)leadboat(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, Dorian Hoxha <dorian(dot)hoxha(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com> |
| Subject: | Re: Alter timestamp without timezone to with timezone rewrites rows |
| Date: | 2021-01-17 00:20:55 |
| Message-ID: | 20210117002055.GA1695558@rfd.leadboat.com |
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| Lists: | pgsql-hackers |
On Sat, Jan 16, 2021 at 12:03:19PM -0500, Tom Lane wrote:
> Noah Misch <noah(at)leadboat(dot)com> writes:
> > On Wed, Jan 13, 2021 at 10:28:26AM -0500, Tom Lane wrote:
> >> So a non-rewriting conversion would only be possible if local time is
> >> identical to UTC; which is true for few enough people that nobody has
> >> bothered with attempting the optimization.
>
> > PostgreSQL 12 and later do have that optimization. Example DDL:
> > https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=3c59263#patch4
>
> Ah, I'd forgotten about that patch (obviously). It is a kluge, without
> a doubt, since it has to hard-wire knowledge about the behavior of two
> specific conversions into what ought to be general-purpose code. But
> I guess it is useful often enough to justify its existence.
>
> I wonder whether it'd be worth moving this logic into a planner support
> function attached to those conversion functions? I wouldn't bother
> right now, but if somebody else comes along with a similar proposal,
> we should think hard about that.
Yes.
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