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Re: Re: logical changeset generation v3 - comparison to Postgres-R change set format

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Hannu Krosing <hannu(at)2ndQuadrant(dot)com>
Cc: Noah Misch <noah(at)leadboat(dot)com>, Markus Wanner <markus(at)bluegap(dot)ch>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Re: logical changeset generation v3 - comparison to Postgres-R change set format
Date: 2013-01-13 17:44:44
Message-ID: 12656.1358099084@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Hannu Krosing <hannu(at)2ndQuadrant(dot)com> writes:
> How do people feel about adding a real sameness operator ?

Just begs the question of "what's sameness?"

In many places we consider a datatype's default btree equality operator
to define sameness, but not all types provide a btree opclass (in
particular, anything that hasn't got a sensible one-dimensional sort
order will not).  And some do but it doesn't represent anything that
anyone would want to consider "sameness" --- IIRC, some of the geometric
types provide btree opclasses that sort by area.  Even for apparently
simple types like float8 there are interesting questions like whether
minus zero is the same as plus zero.

The messiness here is not just due to lack of a notation.

			regards, tom lane


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