Re: [PATCH] Improve geometric types

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Cc: emre(at)hasegeli(dot)com, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: [PATCH] Improve geometric types
Date: 2018-09-26 22:48:47
Message-ID: 6428.1538002127@sss.pgh.pa.us
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Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
> On 09/26/2018 06:45 PM, Tom Lane wrote:
>> gaur's not happy, but rather surprisingly, it looks like we're
>> mostly OK elsewhere. Do you need me to trace down exactly what's
>> going wrong on gaur?

> Or you could just try doing
> select '(0,0)'::point * '(-3,4)'::point;
> If this is what's going on, I'd say the best solution is to make it
> produce (0,0) everywhere, so that we don't expect -0.0 anywhere.

Actually, it seems simpler than that: gaur produces plus zero already
from the multiplication:

regression=# select '-3'::float8 * '0'::float8;
?column?
----------
0
(1 row)

whereas I get -0 elsewhere. I'm surprised that this doesn't create
more widely-visible regression failures, but there you have it.

> We could do that either by adding the == 0.0 check to yet another place,
> or to point_construct() directly. Adding it to point_construct() means
> we'll pay the price always, but I guess there are few paths where we
> know we don't need it. And if we add it to many places it's likely about
> as expensive as adding it to point_construct.

If gaur is the only machine showing this failure, which seems more
likely by the hour, I'm not sure that we should give up performance
across-the-board to make it happy. Perhaps a variant expected-file
is a better answer; or we could remove these specific test cases.

Anyway, I'd counsel doing nothing for a day or so, till the buildfarm
breakage from the strerror/snprintf changes clears up. Then we'll
have a better idea of whether any other machines are affected.

regards, tom lane

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