From: | Juan José Santamaría Flecha <juanjo(dot)santamaria(at)gmail(dot)com> |
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To: | Peter Geoghegan <pg(at)bowt(dot)ie> |
Cc: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Daniel Verite <daniel(at)manitou-mail(dot)org>, Joe Conway <mail(at)joeconway(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Inconsistent results with libc sorting on Windows |
Date: | 2023-06-14 10:50:28 |
Message-ID: | CAC+AXB2ZNhK+60xtBHP935LXjN4PkU-FGBKEy20RHKG=Ysq5hA@mail.gmail.com |
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Lists: | pgsql-hackers |
On Wed, Jun 14, 2023 at 4:13 AM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> On Tue, Jun 13, 2023 at 5:59 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
> wrote:
> > Trying to follow along here... you're doing the moral equivalent of
> > strxfrm(), so sort keys have the transitive property but direct string
> > comparisons don't? Or is this because LCIDs reach a different
> > algorithm somehow (or otherwise why do you need to use LCIDs for this,
> > when there is a non-LCID version of that function, with a warning not
> > to use the older LCID version[1]?)
>
> I'm reminded of the fact that the abbreviated keys strxfrm() debacle
> (back when 9.5 was released) was caused by a bug in strcoll() -- not a
> bug in strxfrm() itself. From our point of view the problem was that
> strxfrm() failed to be bug compatible with strcoll() due to a buggy
> strcoll() optimization.
>
> I believe that strxfrm() is generally less likely to have bugs than
> strcoll(). There are far fewer opportunities to dodge unnecessary work
> in the case of strxfrm()-like algorithms (offering something like
> ICU's pg_strnxfrm_prefix_icu() prefix optimization is the only one).
> On the other hand, collation library implementers are likely to
> heavily optimize strcoll() for typical use-cases such as sorting and
> binary search. Using strxfrm() for everything is discouraged [1].
>
Yes, I think the situation is quite similar to what you describe, with its
WIN32 peculiarities. Take for example the attached program, it'll output:
s1 = s2
s2 = s3
s1 > s3
c1 > c2
c2 > c3
c1 > c3
As you can see the test for CompareStringEx() is broken, but we get a sane
answer with LCMapStringEx().
Regards,
Juan José Santamaría Flecha
Attachment | Content-Type | Size |
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compare_transitivity.c | application/octet-stream | 1.4 KB |
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