Re: Odd 9.4, 9.3 buildfarm failure on s390x

On Tue, Oct 2, 2018 at 10:55 AM Andrew Dunstan
<andrew.dunstan@2ndquadrant.com> wrote:
> On 10/01/2018 12:50 PM, Tom Lane wrote:
> > Andres Freund <andres@anarazel.de> writes:
> >> On 2018-10-01 12:13:57 -0400, Tom Lane wrote:
> >>> Yeah.  So our choices are
> >>>
> >>> (1) Retain the current restriction on what sort comparators can
> >>> produce.  Find all the places where memcmp's result is returned
> >>> directly, and fix them.  (I wonder if strcmp has same issue.)
> >>>
> >>> (2) Drop the restriction.  This'd require at least changing the
> >>> DESC correction, and maybe other things.  I'm not sure what the
> >>> odds would be of finding everyplace we need to check.
> >>>
> >>> Neither one is sounding very pleasant, or maintainable.
> >> (2) seems more maintainable to me (or perhaps less unmaintainable). It's
> >> infrastructure, rather than every datatype + support out there...
> > I guess we could set up some testing infrastructure: hack int4cmp
> > and/or a couple other popular comparators so that they *always*
> > return INT_MIN, 0, or INT_MAX, and then see what falls over.
> >
> > I'm fairly sure that btree, as well as the sort code proper,
> > has got an issue here.
> >
> >
>
>
> I agree option 2 seems less unmaintainable. (Nice use of litotes there?)

+1 for option 2.  It seems to me that it should ideally be the job of
the code that is negating the value to deal with this edge case.  I
see that the restriction is clearly documented at the top of
src/backend/access/nbtree/nbtcompare.c even though it directly returns
strncmp() results.  This was quite a surprising thread.

-- 
Thomas Munro
http://www.enterprisedb.com