Re: More stable query plans via more predictable column statistics

Alex Shulgin <alex.shulgin@gmail.com> writes:
> On Sun, Apr 3, 2016 at 7:49 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> If there is only one value, it will have 100% of the samples, so it would
>> get included under just about any decision rule (other than "more than
>> 100% of this value plus following values").  I don't think making sure
>> this case works is sufficient to get us to a reasonable rule --- it's
>> a necessary case, but not a sufficient case.

> Well, if it's the only value it will be accepted simply because we are
> checking that special case already and don't even bother to loop through
> the track list.

That was demonstrably not the case in the failing regression test.
I forget what aspect of the test case allowed it to get past the short
circuit, but it definitely got into the scan-the-track-list code.
        regards, tom lane