/*
** The GiST Penalty method for segments
** As in the R-tree paper, we use change in area as our penalty metric
*/
float *
gseg_penalty(GISTENTRY *origentry, GISTENTRY *newentry, float *result)
{
SEG *ud;
float tmp1,
tmp2;
ud = seg_union((SEG *) DatumGetPointer(origentry->key),
(SEG *) DatumGetPointer(newentry->key));
rt_seg_size(ud, &tmp1);
rt_seg_size((SEG *) DatumGetPointer(origentry->key), &tmp2);
*result = tmp1 - tmp2;
#ifdef GIST_DEBUG
fprintf(stderr, "penalty\n");
fprintf(stderr, "\t%g\n", *result);
#endif
return (result);
}
/*
** The GiST PickSplit method for segments
** We use Guttman's poly time split algorithm
*/
GIST_SPLITVEC *
gseg_picksplit(GistEntryVector *entryvec,
GIST_SPLITVEC *v)
{
OffsetNumber i,
j;
SEG *datum_alpha,
*datum_beta;
SEG *datum_l,
*datum_r;
SEG *union_d,
*union_dl,
*union_dr;
SEG *inter_d;
bool firsttime;
float size_alpha,
size_beta,
size_union,
size_inter;
float size_waste,
waste;
float size_l,
size_r;
int nbytes;
OffsetNumber seed_1 = 1,
seed_2 = 2;
OffsetNumber *left,
*right;
OffsetNumber maxoff;
#ifdef GIST_DEBUG
fprintf(stderr, "picksplit\n");
#endif
maxoff = entryvec->n - 2;
nbytes = (maxoff + 2) * sizeof(OffsetNumber);
v->spl_left = (OffsetNumber *) palloc(nbytes);
v->spl_right = (OffsetNumber *) palloc(nbytes);
firsttime = true;
waste = 0.0;
for (i = FirstOffsetNumber; i < maxoff; i = OffsetNumberNext(i))
{
datum_alpha = (SEG *) DatumGetPointer(entryvec->vector[i].key);
for (j = OffsetNumberNext(i); j <= maxoff; j = OffsetNumberNext(j))
{
datum_beta = (SEG *) DatumGetPointer(entryvec->vector[j].key);
/* compute the wasted space by unioning these guys */
/* size_waste = size_union - size_inter; */
union_d = seg_union(datum_alpha, datum_beta);
rt_seg_size(union_d, &size_union);
inter_d = seg_inter(datum_alpha, datum_beta);
rt_seg_size(inter_d, &size_inter);
size_waste = size_union - size_inter;
/*
* are these a more promising split that what we've already seen?
*/
if (size_waste > waste || firsttime)
{
waste = size_waste;
seed_1 = i;
seed_2 = j;
firsttime = false;
}
}
}
left = v->spl_left;
v->spl_nleft = 0;
right = v->spl_right;
v->spl_nright = 0;
datum_alpha = (SEG *) DatumGetPointer(entryvec->vector[seed_1].key);
datum_l = seg_union(datum_alpha, datum_alpha);
rt_seg_size(datum_l, &size_l);
datum_beta = (SEG *) DatumGetPointer(entryvec->vector[seed_2].key);
datum_r = seg_union(datum_beta, datum_beta);
rt_seg_size(datum_r, &size_r);
/*
* Now split up the regions between the two seeds. An important property
* of this split algorithm is that the split vector v has the indices of
* items to be split in order in its left and right vectors. We exploit
* this property by doing a merge in the code that actually splits the
* page.
*
* For efficiency, we also place the new index tuple in this loop. This is
* handled at the very end, when we have placed all the existing tuples
* and i == maxoff + 1.
*/
maxoff = OffsetNumberNext(maxoff);
for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
{
/*
* If we've already decided where to place this item, just put it on
* the right list. Otherwise, we need to figure out which page needs
* the least enlargement in order to store the item.
*/
if (i == seed_1)
{
*left++ = i;
v->spl_nleft++;
continue;
}
else if (i == seed_2)
{
*right++ = i;
v->spl_nright++;
continue;
}
/* okay, which page needs least enlargement? */
datum_alpha = (SEG *) DatumGetPointer(entryvec->vector[i].key);
union_dl = seg_union(datum_l, datum_alpha);
union_dr = seg_union(datum_r, datum_alpha);
rt_seg_size(union_dl, &size_alpha);
rt_seg_size(union_dr, &size_beta);
/* pick which page to add it to */
if (size_alpha - size_l < size_beta - size_r)
{
datum_l = union_dl;
size_l = size_alpha;
*left++ = i;
v->spl_nleft++;
}
else
{
datum_r = union_dr;
size_r = size_alpha;
*right++ = i;
v->spl_nright++;
}
}
*left = *right = FirstOffsetNumber; /* sentinel value, see dosplit() */
v->spl_ldatum = PointerGetDatum(datum_l);
v->spl_rdatum = PointerGetDatum(datum_r);
return v;
}