Re: Fix for seg picksplit function

On Mon, Nov 15, 2010 at 4:06 AM, Alexander Korotkov
<aekorotkov(at)gmail(dot)com> wrote:
> With help of Oleg I found, that line "*left = *right = FirstOffsetNumber;"
> was needed only for 7.X compatibility, and it isn't needed any more.
> Also, I've replaced "i - 1" by "i - FirstOffsetNumber" in array filling.
> I believe it's more correct way, because it'll work correctly in the case
> when FirstOffsetNumber alters.

The loop that begins here:

for (i = 0; i < maxoff; i++)
{
/* First half of segs goes to the left datum. */
if (i < seed_2)

...looks like it should perhaps be broken into two separate loops.
That might also help tweak the logic in a way that eliminates this:

seg.c: In function ‘gseg_picksplit’:
seg.c:327: warning: ‘datum_r’ may be used uninitialized in this function
seg.c:326: warning: ‘datum_l’ may be used uninitialized in this function

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."

--
Robert Haas
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