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Replace the "New Linear" GiST split algorithm for boxes and points with a

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new double-sorting algorithm. The new algorithm produces better quality
trees, making searches faster.

Alexander Korotkov
pull/1/head
Heikki Linnakangas 14 years ago
parent ba6f629326
commit 7f3bd86843
1 changed files with 557 additions and 254 deletions
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  1. 811
      src/backend/access/gist/gistproc.c

811
src/backend/access/gist/gistproc.c
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@ -27,6 +27,9 @@ static double size_box(Datum dbox);
static bool rtree_internal_consistent(BOX *key, BOX *query,
StrategyNumber strategy);
/* Minimum accepted ratio of split */
#define LIMIT_RATIO 0.3
/**************************************************
* Box ops
@ -49,30 +52,6 @@ rt_box_union(PG_FUNCTION_ARGS)
PG_RETURN_BOX_P(n);
}
static Datum
rt_box_inter(PG_FUNCTION_ARGS)
{
BOX *a = PG_GETARG_BOX_P(0);
BOX *b = PG_GETARG_BOX_P(1);
BOX *n;
n = (BOX *) palloc(sizeof(BOX));
n->high.x = Min(a->high.x, b->high.x);
n->high.y = Min(a->high.y, b->high.y);
n->low.x = Max(a->low.x, b->low.x);
n->low.y = Max(a->low.y, b->low.y);
if (n->high.x < n->low.x || n->high.y < n->low.y)
{
pfree(n);
/* Indicate "no intersection" by returning NULL pointer */
n = NULL;
}
PG_RETURN_BOX_P(n);
}
/*
* The GiST Consistent method for boxes
*
@ -194,86 +173,6 @@ gist_box_penalty(PG_FUNCTION_ARGS)
PG_RETURN_POINTER(result);
}
static void
chooseLR(GIST_SPLITVEC *v,
OffsetNumber *list1, int nlist1, BOX *union1,
OffsetNumber *list2, int nlist2, BOX *union2)
{
bool firstToLeft = true;
if (v->spl_ldatum_exists || v->spl_rdatum_exists)
{
if (v->spl_ldatum_exists && v->spl_rdatum_exists)
{
BOX LRl = *union1,
LRr = *union2;
BOX RLl = *union2,
RLr = *union1;
double sizeLR,
sizeRL;
adjustBox(&LRl, DatumGetBoxP(v->spl_ldatum));
adjustBox(&LRr, DatumGetBoxP(v->spl_rdatum));
adjustBox(&RLl, DatumGetBoxP(v->spl_ldatum));
adjustBox(&RLr, DatumGetBoxP(v->spl_rdatum));
sizeLR = size_box(DirectFunctionCall2(rt_box_inter, BoxPGetDatum(&LRl), BoxPGetDatum(&LRr)));
sizeRL = size_box(DirectFunctionCall2(rt_box_inter, BoxPGetDatum(&RLl), BoxPGetDatum(&RLr)));
if (sizeLR > sizeRL)
firstToLeft = false;
}
else
{
float p1,
p2;
GISTENTRY oldUnion,
addon;
gistentryinit(oldUnion, (v->spl_ldatum_exists) ? v->spl_ldatum : v->spl_rdatum,
NULL, NULL, InvalidOffsetNumber, FALSE);
gistentryinit(addon, BoxPGetDatum(union1), NULL, NULL, InvalidOffsetNumber, FALSE);
DirectFunctionCall3(gist_box_penalty, PointerGetDatum(&oldUnion), PointerGetDatum(&addon), PointerGetDatum(&p1));
gistentryinit(addon, BoxPGetDatum(union2), NULL, NULL, InvalidOffsetNumber, FALSE);
DirectFunctionCall3(gist_box_penalty, PointerGetDatum(&oldUnion), PointerGetDatum(&addon), PointerGetDatum(&p2));
if ((v->spl_ldatum_exists && p1 > p2) || (v->spl_rdatum_exists && p1 < p2))
firstToLeft = false;
}
}
if (firstToLeft)
{
v->spl_left = list1;
v->spl_right = list2;
v->spl_nleft = nlist1;
v->spl_nright = nlist2;
if (v->spl_ldatum_exists)
adjustBox(union1, DatumGetBoxP(v->spl_ldatum));
v->spl_ldatum = BoxPGetDatum(union1);
if (v->spl_rdatum_exists)
adjustBox(union2, DatumGetBoxP(v->spl_rdatum));
v->spl_rdatum = BoxPGetDatum(union2);
}
else
{
v->spl_left = list2;
v->spl_right = list1;
v->spl_nleft = nlist2;
v->spl_nright = nlist1;
if (v->spl_ldatum_exists)
adjustBox(union2, DatumGetBoxP(v->spl_ldatum));
v->spl_ldatum = BoxPGetDatum(union2);
if (v->spl_rdatum_exists)
adjustBox(union1, DatumGetBoxP(v->spl_rdatum));
v->spl_rdatum = BoxPGetDatum(union1);
}
v->spl_ldatum_exists = v->spl_rdatum_exists = false;
}
/*
* Trivial split: half of entries will be placed on one page
* and another half - to another
@ -338,199 +237,603 @@ fallbackSplit(GistEntryVector *entryvec, GIST_SPLITVEC *v)
}
/*
* The GiST PickSplit method
* Represents information about an entry that can be placed to either group
* without affecting overlap over selected axis ("common entry").
*/
typedef struct
{
/* Index of entry in the initial array */
int index;
/* Delta between penalties of entry insertion into different groups */
double delta;
} CommonEntry;
/*
* Context for g_box_consider_split. Contains information about currently
* selected split and some general information.
*/
typedef struct
{
int entriesCount; /* total number of entries being split */
BOX boundingBox; /* minimum bounding box across all entries */
/* Information about currently selected split follows */
bool first; /* true if no split was selected yet */
double leftUpper; /* upper bound of left interval */
double rightLower; /* lower bound of right interval */
float4 ratio;
float4 overlap;
int dim; /* axis of this split */
double range; /* width of general MBR projection to the
* selected axis */
} ConsiderSplitContext;
/*
* Interval represents projection of box to axis.
*/
typedef struct
{
double lower,
upper;
} SplitInterval;
/*
* Interval comparison function by lower bound of the interval;
*/
static int
interval_cmp_lower(const void *i1, const void *i2)
{
double lower1 = ((SplitInterval *) i1)->lower,
lower2 = ((SplitInterval *) i2)->lower;
if (lower1 < lower2)
return -1;
else if (lower1 > lower2)
return 1;
else
return 0;
}
/*
* Interval comparison function by upper bound of the interval;
*/
static int
interval_cmp_upper(const void *i1, const void *i2)
{
double upper1 = ((SplitInterval *) i1)->upper,
upper2 = ((SplitInterval *) i2)->upper;
if (upper1 < upper2)
return -1;
else if (upper1 > upper2)
return 1;
else
return 0;
}
/*
* Replace negative value with zero.
*/
static inline float
non_negative(float val)
{
if (val >= 0.0f)
return val;
else
return 0.0f;
}
/*
* Consider replacement of currently selected split with the better one.
*/
static void inline
g_box_consider_split(ConsiderSplitContext *context, int dimNum,
double rightLower, int minLeftCount,
double leftUpper, int maxLeftCount)
{
int leftCount,
rightCount;
float4 ratio,
overlap;
double range;
/*
* Calculate entries distribution ratio assuming most uniform distribution
* of common entries.
*/
if (minLeftCount >= (context->entriesCount + 1) / 2)
{
leftCount = minLeftCount;
}
else
{
if (maxLeftCount <= context->entriesCount / 2)
leftCount = maxLeftCount;
else
leftCount = context->entriesCount / 2;
}
rightCount = context->entriesCount - leftCount;
/*
* Ratio of split - quotient between size of lesser group and total
* entries count.
*/
ratio = ((float4) Min(leftCount, rightCount)) /
((float4) context->entriesCount);
if (ratio > LIMIT_RATIO)
{
bool selectthis = false;
/*
* The ratio is acceptable, so compare current split with previously
* selected one. Between splits of one dimension we search for minimal
* overlap (allowing negative values) and minimal ration (between same
* overlaps. We switch dimension if find less overlap (non-negative)
* or less range with same overlap.
*/
if (dimNum == 0)
range = context->boundingBox.high.x - context->boundingBox.low.x;
else
range = context->boundingBox.high.y - context->boundingBox.low.y;
overlap = (leftUpper - rightLower) / range;
/* If there is no previous selection, select this */
if (context->first)
selectthis = true;
else if (context->dim == dimNum)
{
/*
* Within the same dimension, choose the new split if it has a
* smaller overlap, or same overlap but better ratio.
*/
if (overlap < context->overlap ||
(overlap == context->overlap && ratio > context->ratio))
selectthis = true;
}
else
{
/*
* Across dimensions, choose the new split if it has a smaller
* *non-negative* overlap, or same *non-negative* overlap but
* bigger range. This condition differs from the one described in
* the article. On the datasets where leaf MBRs don't overlap
* themselves, non-overlapping splits (i.e. splits which have zero
* *non-negative* overlap) are frequently possible. In this case
* splits tends to be along one dimension, because most distant
* non-overlapping splits (i.e. having lowest negative overlap)
* appears to be in the same dimension as in the previous split.
* Therefore MBRs appear to be very prolonged along another
* dimension, which leads to bad search performance. Using range
* as the second split criteria makes MBRs more quadratic. Using
* *non-negative* overlap instead of overlap as the first split
* criteria gives to range criteria a chance to matter, because
* non-overlapping splits are equivalent in this criteria.
*/
if (non_negative(overlap) < non_negative(context->overlap) ||
(range > context->range &&
non_negative(overlap) <= non_negative(context->overlap)))
selectthis = true;
}
if (selectthis)
{
/* save information about selected split */
context->first = false;
context->ratio = ratio;
context->range = range;
context->overlap = overlap;
context->rightLower = rightLower;
context->leftUpper = leftUpper;
context->dim = dimNum;
}
}
}
/*
* Return increase of original BOX area by new BOX area insertion.
*/
static double
box_penalty(BOX *original, BOX *new)
{
double union_width,
union_height;
union_width = Max(original->high.x, new->high.x) -
Min(original->low.x, new->low.x);
union_height = Max(original->high.y, new->high.y) -
Min(original->low.y, new->low.y);
return union_width * union_height - (original->high.x - original->low.x) *
(original->high.y - original->low.y);
}
/*
* Compare common entries by their deltas.
*/
static int
common_entry_cmp(const void *i1, const void *i2)
{
double delta1 = ((CommonEntry *) i1)->delta,
delta2 = ((CommonEntry *) i2)->delta;
if (delta1 < delta2)
return -1;
else if (delta1 > delta2)
return 1;
else
return 0;
}
/*
* --------------------------------------------------------------------------
* Double sorting split algorithm. This is used for both boxes and points.
*
* New linear algorithm, see 'New Linear Node Splitting Algorithm for R-tree',
* C.H.Ang and T.C.Tan
* The algorithm finds split of boxes by considering splits along each axis.
* Each entry is first projected as an interval on the X-axis, and different
* ways to split the intervals into two groups are considered, trying to
* minimize the overlap of the groups. Then the same is repeated for the
* Y-axis, and the overall best split is chosen. The quality of a split is
* determined by overlap along that axis and some other criteria (see
* g_box_consider_split).
*
* This is used for both boxes and points.
* After that, all the entries are divided into three groups:
*
* 1) Entries which should be placed to the left group
* 2) Entries which should be placed to the right group
* 3) "Common entries" which can be placed to any of groups without affecting
* of overlap along selected axis.
*
* The common entries are distributed by minimizing penalty.
*
* For details see:
* "A new double sorting-based node splitting algorithm for R-tree", A. Korotkov
* http://syrcose.ispras.ru/2011/files/SYRCoSE2011_Proceedings.pdf#page=36
* --------------------------------------------------------------------------
*/
Datum
gist_box_picksplit(PG_FUNCTION_ARGS)
{
GistEntryVector *entryvec = (GistEntryVector *) PG_GETARG_POINTER(0);
GIST_SPLITVEC *v = (GIST_SPLITVEC *) PG_GETARG_POINTER(1);
OffsetNumber i;
OffsetNumber *listL,
*listR,
*listB,
*listT;
BOX *unionL,
*unionR,
*unionB,
*unionT;
int posL,
posR,
posB,
posT;
BOX pageunion;
BOX *cur;
char direction = ' ';
bool allisequal = true;
OffsetNumber maxoff;
int nbytes;
OffsetNumber i,
maxoff;
ConsiderSplitContext context;
BOX *box,
*leftBox,
*rightBox;
int dim,
commonEntriesCount;
SplitInterval *intervalsLower,
*intervalsUpper;
CommonEntry *commonEntries;
int nentries;
memset(&context, 0, sizeof(ConsiderSplitContext));
posL = posR = posB = posT = 0;
maxoff = entryvec->n - 1;
nentries = context.entriesCount = maxoff - FirstOffsetNumber + 1;
cur = DatumGetBoxP(entryvec->vector[FirstOffsetNumber].key);
memcpy((void *) &pageunion, (void *) cur, sizeof(BOX));
/* Allocate arrays for intervals along axes */
intervalsLower = (SplitInterval *) palloc(nentries * sizeof(SplitInterval));
intervalsUpper = (SplitInterval *) palloc(nentries * sizeof(SplitInterval));
/* find MBR */
for (i = OffsetNumberNext(FirstOffsetNumber); i <= maxoff; i = OffsetNumberNext(i))
/*
* Calculate the overall minimum bounding box over all the entries.
*/
for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
{
cur = DatumGetBoxP(entryvec->vector[i].key);
if (allisequal && (
pageunion.high.x != cur->high.x ||
pageunion.high.y != cur->high.y ||
pageunion.low.x != cur->low.x ||
pageunion.low.y != cur->low.y
))
allisequal = false;
adjustBox(&pageunion, cur);
box = DatumGetBoxP(entryvec->vector[i].key);
if (i == FirstOffsetNumber)
context.boundingBox = *box;
else
adjustBox(&context.boundingBox, box);
}
if (allisequal)
/*
* Iterate over axes for optimal split searching.
*/
context.first = true; /* nothing selected yet */
for (dim = 0; dim < 2; dim++)
{
double leftUpper,
rightLower;
int i1,
i2;
/* Project each entry as an interval on the selected axis. */
for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
{
box = DatumGetBoxP(entryvec->vector[i].key);
if (dim == 0)
{
intervalsLower[i - FirstOffsetNumber].lower = box->low.x;
intervalsLower[i - FirstOffsetNumber].upper = box->high.x;
}
else
{
intervalsLower[i - FirstOffsetNumber].lower = box->low.y;
intervalsLower[i - FirstOffsetNumber].upper = box->high.y;
}
}
/*
* Make two arrays of intervals: one sorted by lower bound and another
* sorted by upper bound.
*/
memcpy(intervalsUpper, intervalsLower,
sizeof(SplitInterval) * nentries);
qsort(intervalsLower, nentries, sizeof(SplitInterval),
interval_cmp_lower);
qsort(intervalsUpper, nentries, sizeof(SplitInterval),
interval_cmp_upper);
/*----
* The goal is to form a left and right interval, so that every entry
* interval is contained by either left or right interval (or both).
*
* For example, with the intervals (0,1), (1,3), (2,3), (2,4):
*
* 0 1 2 3 4
* +-+
* +---+
* +-+
* +---+
*
* The left and right intervals are of the form (0,a) and (b,4).
* We first consider splits where b is the lower bound of an entry.
* We iterate through all entries, and for each b, calculate the
* smallest possible a. Then we consider splits where a is the
* uppper bound of an entry, and for each a, calculate the greatest
* possible b.
*
* In the above example, the first loop would consider splits:
* b=0: (0,1)-(0,4)
* b=1: (0,1)-(1,4)
* b=2: (0,3)-(2,4)
*
* And the second loop:
* a=1: (0,1)-(1,4)
* a=3: (0,3)-(2,4)
* a=4: (0,4)-(2,4)
*/
/*
* Iterate over lower bound of right group, finding smallest possible
* upper bound of left group.
*/
i1 = 0;
i2 = 0;
rightLower = intervalsLower[i1].lower;
leftUpper = intervalsUpper[i2].lower;
while (true)
{
/*
* Find next lower bound of right group.
*/
while (i1 < nentries && rightLower == intervalsLower[i1].lower)
{
leftUpper = Max(leftUpper, intervalsLower[i1].upper);
i1++;
}
if (i1 >= nentries)
break;
rightLower = intervalsLower[i1].lower;
/*
* Find count of intervals which anyway should be placed to the
* left group.
*/
while (i2 < nentries && intervalsUpper[i2].upper <= leftUpper)
i2++;
/*
* Consider found split.
*/
g_box_consider_split(&context, dim, rightLower, i1, leftUpper, i2);
}
/*
* All entries are the same
* Iterate over upper bound of left group finding greates possible
* lower bound of right group.
*/
i1 = nentries - 1;
i2 = nentries - 1;
rightLower = intervalsLower[i1].upper;
leftUpper = intervalsUpper[i2].upper;
while (true)
{
/*
* Find next upper bound of left group.
*/
while (i2 >= 0 && leftUpper == intervalsUpper[i2].upper)
{
rightLower = Min(rightLower, intervalsUpper[i2].lower);
i2--;
}
if (i2 < 0)
break;
leftUpper = intervalsUpper[i2].upper;
/*
* Find count of intervals which anyway should be placed to the
* right group.
*/
while (i1 >= 0 && intervalsLower[i1].lower >= rightLower)
i1--;
/*
* Consider found split.
*/
g_box_consider_split(&context, dim,
rightLower, i1 + 1, leftUpper, i2 + 1);
}
}
/*
* If we failed to find any acceptable splits, use trivial split.
*/
if (context.first)
{
fallbackSplit(entryvec, v);
PG_RETURN_POINTER(v);
}
nbytes = (maxoff + 2) * sizeof(OffsetNumber);
listL = (OffsetNumber *) palloc(nbytes);
listR = (OffsetNumber *) palloc(nbytes);
listB = (OffsetNumber *) palloc(nbytes);
listT = (OffsetNumber *) palloc(nbytes);
unionL = (BOX *) palloc(sizeof(BOX));
unionR = (BOX *) palloc(sizeof(BOX));
unionB = (BOX *) palloc(sizeof(BOX));
unionT = (BOX *) palloc(sizeof(BOX));
#define ADDLIST( list, unionD, pos, num ) do { \
if ( pos ) { \
if ( (unionD)->high.x < cur->high.x ) (unionD)->high.x = cur->high.x; \
if ( (unionD)->low.x > cur->low.x ) (unionD)->low.x = cur->low.x; \
if ( (unionD)->high.y < cur->high.y ) (unionD)->high.y = cur->high.y; \
if ( (unionD)->low.y > cur->low.y ) (unionD)->low.y = cur->low.y; \
} else { \
memcpy( (void*)(unionD), (void*) cur, sizeof( BOX ) ); \
} \
(list)[pos] = num; \
(pos)++; \
} while(0)
/*
* Ok, we have now selected the split across one axis.
*
* While considering the splits, we already determined that there will be
* enough entries in both groups to reach the desired ratio, but we did
* not memorize which entries go to which group. So determine that now.
*/
for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
{
cur = DatumGetBoxP(entryvec->vector[i].key);
if (cur->low.x - pageunion.low.x < pageunion.high.x - cur->high.x)
ADDLIST(listL, unionL, posL, i);
else
ADDLIST(listR, unionR, posR, i);
if (cur->low.y - pageunion.low.y < pageunion.high.y - cur->high.y)
ADDLIST(listB, unionB, posB, i);
else
ADDLIST(listT, unionT, posT, i);
}
/* Allocate vectors for results */
v->spl_left = (OffsetNumber *) palloc(nentries * sizeof(OffsetNumber));
v->spl_right = (OffsetNumber *) palloc(nentries * sizeof(OffsetNumber));
v->spl_nleft = 0;
v->spl_nright = 0;
/* Allocate bounding boxes of left and right groups */
leftBox = palloc0(sizeof(BOX));
rightBox = palloc0(sizeof(BOX));
#define LIMIT_RATIO 0.1
#define _IS_BADRATIO(x,y) ( (y) == 0 || (float)(x)/(float)(y) < LIMIT_RATIO )
#define IS_BADRATIO(x,y) ( _IS_BADRATIO((x),(y)) || _IS_BADRATIO((y),(x)) )
/* bad disposition, try to split by centers of boxes */
if (IS_BADRATIO(posR, posL) && IS_BADRATIO(posT, posB))
/*
* Allocate an array for "common entries" - entries which can be placed to
* either group without affecting overlap along selected axis.
*/
commonEntriesCount = 0;
commonEntries = (CommonEntry *) palloc(nentries * sizeof(CommonEntry));
/* Helper macros to place an entry in the left or right group */
#define PLACE_LEFT(box, off) \
do { \
if (v->spl_nleft > 0) \
adjustBox(leftBox, box); \
else \
*leftBox = *(box); \
v->spl_left[v->spl_nleft++] = off; \
} while(0)
#define PLACE_RIGHT(box, off) \
do { \
if (v->spl_nright > 0) \
adjustBox(rightBox, box); \
else \
*rightBox = *(box); \
v->spl_right[v->spl_nright++] = off; \
} while(0)
/*
* Distribute entries which can be distributed unambiguously, and collect
* common entries.
*/
for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
{
double avgCenterX = 0.0,
avgCenterY = 0.0;
double CenterX,
CenterY;
double lower,
upper;
for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
/*
* Get upper and lower bounds along selected axis.
*/
box = DatumGetBoxP(entryvec->vector[i].key);
if (context.dim == 0)
{
cur = DatumGetBoxP(entryvec->vector[i].key);
avgCenterX += ((double) cur->high.x + (double) cur->low.x) / 2.0;
avgCenterY += ((double) cur->high.y + (double) cur->low.y) / 2.0;
lower = box->low.x;
upper = box->high.x;
}
avgCenterX /= maxoff;
avgCenterY /= maxoff;
posL = posR = posB = posT = 0;
for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
else
{
cur = DatumGetBoxP(entryvec->vector[i].key);
CenterX = ((double) cur->high.x + (double) cur->low.x) / 2.0;
CenterY = ((double) cur->high.y + (double) cur->low.y) / 2.0;
lower = box->low.y;
upper = box->high.y;
}
if (CenterX < avgCenterX)
ADDLIST(listL, unionL, posL, i);
else if (CenterX == avgCenterX)
if (upper <= context.leftUpper)
{
/* Fits to the left group */
if (lower >= context.rightLower)
{
if (posL > posR)
ADDLIST(listR, unionR, posR, i);
else
ADDLIST(listL, unionL, posL, i);
/* Fits also to the right group, so "common entry" */
commonEntries[commonEntriesCount++].index = i;
}
else
ADDLIST(listR, unionR, posR, i);
if (CenterY < avgCenterY)
ADDLIST(listB, unionB, posB, i);
else if (CenterY == avgCenterY)
{
if (posB > posT)
ADDLIST(listT, unionT, posT, i);
else
ADDLIST(listB, unionB, posB, i);
/* Doesn't fit to the right group, so join to the left group */
PLACE_LEFT(box, i);
}
else
ADDLIST(listT, unionT, posT, i);
}
if (IS_BADRATIO(posR, posL) && IS_BADRATIO(posT, posB))
else
{
fallbackSplit(entryvec, v);
PG_RETURN_POINTER(v);
/*
* Each entry should fit on either left or right group. Since this
* entry didn't fit on the left group, it better fit in the right
* group.
*/
Assert(lower >= context.rightLower);
/* Doesn't fit to the left group, so join to the right group */
PLACE_RIGHT(box, i);
}
}
/* which split more optimal? */
if (Max(posL, posR) < Max(posB, posT))
direction = 'x';
else if (Max(posL, posR) > Max(posB, posT))
direction = 'y';
else
/*
* Distribute "common entries", if any.
*/
if (commonEntriesCount > 0)
{
Datum interLR = DirectFunctionCall2(rt_box_inter,
BoxPGetDatum(unionL),
BoxPGetDatum(unionR));
Datum interBT = DirectFunctionCall2(rt_box_inter,
BoxPGetDatum(unionB),
BoxPGetDatum(unionT));
double sizeLR,
sizeBT;
sizeLR = size_box(interLR);
sizeBT = size_box(interBT);
if (sizeLR < sizeBT)
direction = 'x';
else
direction = 'y';
}
/*
* Calculate minimum number of entries that must be placed in both
* groups, to reach LIMIT_RATIO.
*/
int m = ceil(LIMIT_RATIO * (double) nentries);
if (direction == 'x')
chooseLR(v,
listL, posL, unionL,
listR, posR, unionR);
else
chooseLR(v,
listB, posB, unionB,
listT, posT, unionT);
/*
* Calculate delta between penalties of join "common entries" to
* different groups.
*/
for (i = 0; i < commonEntriesCount; i++)
{
box = DatumGetBoxP(entryvec->vector[commonEntries[i].index].key);
commonEntries[i].delta = Abs(box_penalty(leftBox, box) -
box_penalty(rightBox, box));
}
/*
* Sort "common entries" by calculated deltas in order to distribute
* the most ambiguous entries first.
*/
qsort(commonEntries, commonEntriesCount, sizeof(CommonEntry), common_entry_cmp);
/*
* Distribute "common entries" between groups.
*/
for (i = 0; i < commonEntriesCount; i++)
{
box = DatumGetBoxP(entryvec->vector[commonEntries[i].index].key);
/*
* Check if we have to place this entry in either group to achieve
* LIMIT_RATIO.
*/
if (v->spl_nleft + (commonEntriesCount - i) <= m)
PLACE_LEFT(box, commonEntries[i].index);
else if (v->spl_nright + (commonEntriesCount - i) <= m)
PLACE_RIGHT(box, commonEntries[i].index);
else
{
/* Otherwise select the group by minimal penalty */
if (box_penalty(leftBox, box) < box_penalty(rightBox, box))
PLACE_LEFT(box, commonEntries[i].index);
else
PLACE_RIGHT(box, commonEntries[i].index);
}
}
}
v->spl_ldatum = PointerGetDatum(leftBox);
v->spl_rdatum = PointerGetDatum(rightBox);
PG_RETURN_POINTER(v);
}

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