Re: Fix for seg picksplit function

On 2010-11-20 04:46, Robert Haas wrote:
> On Tue, Nov 16, 2010 at 6:07 AM, Alexander Korotkov
> <aekorotkov@gmail.com>  wrote:
>> On Tue, Nov 16, 2010 at 3:07 AM, Robert Haas<robertmhaas@gmail.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.
With the current 8K default blocksize, I put my money on the sorting 
algorithm for any seg case. The r-tree algorithm's performance is 
probably more influenced by large buckets->low tree depth->generic keys 
on non leaf nodes.

regards,
Yeb Havinga