Re: Alter timestamp without timezone to with timezone rewrites rows

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: 2021-01-16 11:53:42
Message-ID: 20210116115342.GA1681052@rfd.leadboat.com
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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

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