Re: [SQL] RE: [GENERAL] Problem with SELECT on large negative INT4

John Brothers <johnbr(at)mindspring(dot)com> writes:
> I don't think that patch will work - Hiroshi whipped up that patch for
> me a week ago for a different problem - we have a table with duplicate
> primary keys, which seems to be an arithmetic overflow problem because
> the index key values can be both very large positive and very large
> negative numbers.

Actually, if Nicolas' table contains both very large positive and very
large negative integers, then his index could be messed up pretty badly.
What Hiroshi saw (and I missed :-() was that btint4cmp can fail and
return a result of the wrong sign if the difference between two integers
overflows. Since index sorting depends critically on the assumption
that the comparator always returns consistent results (a < b and b < c
must imply a < c, but this can fail if a - c overflows), you could have
an out-of-order index. And then probes into the index could fail to
find items they should find ... which is exactly the complained-of
symptom.

Hiroshi neglected to mention that you'd probably need to drop and
recreate the index after applying the patch; if it's indeed out of
order, just patching the comparator bug isn't enough to fix it.

regards, tom lane