Re: Fix for seg picksplit function

On Tue, Nov 16, 2010 at 6:07 AM, Alexander Korotkov
<aekorotkov(at)gmail(dot)com> wrote:
> On Tue, Nov 16, 2010 at 3:07 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> But on a broader note, I'm not very certain the sorting algorithm is
>> sensible.  For example, suppose you have 10 segments that are exactly
>> '0' and 20 segments that are exactly '1'.  Maybe I'm misunderstanding,
>> but it seems like this will result in a 15/15 split when we almost
>> certainly want a 10/20 split.  I think there will be problems in more
>> complex cases as well.  The documentation says about the less-than and
>> greater-than operators that "These operators do not make a lot of
>> sense for any practical purpose but sorting."
>
> In order to illustrate a real problem we should think about
> gist behavior with great enough amount of data. For example, I tried to
> extrapolate this case to 100000 of segs where 40% are (0,1) segs and 60% are
> (1,2) segs. And this case doesn't seem a problem for me.

Well, the problem with just comparing on < is that it takes very
little account of the upper bounds. I think the cases where a simple
split would hurt you the most are those where examining the upper
bound is necessary to to get a good split.

--
Robert Haas
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