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Improve handling of NULLs in KNN-GiST and KNN-SP-GiST

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This commit improves subject in two ways:

 * It removes ugliness of 02f90879e7, which stores distance values and null
   flags in two separate arrays after GISTSearchItem struct.  Instead we pack
   both distance value and null flag in IndexOrderByDistance struct.  Alignment
   overhead should be negligible, because we typically deal with at most few
   "col op const" expressions in ORDER BY clause.
 * It fixes handling of "col op NULL" expression in KNN-SP-GiST.  Now, these
   expression are not passed to support functions, which can't deal with them.
   Instead, NULL result is implicitly assumed.  It future we may decide to
   teach support functions to deal with NULL arguments, but current solution is
   bugfix suitable for backpatch.

Reported-by: Nikita Glukhov
Discussion: https://postgr.es/m/826f57ee-afc7-8977-c44c-6111d18b02ec%40postgrespro.ru
Author: Nikita Glukhov
Reviewed-by: Alexander Korotkov
Backpatch-through: 9.4
This commit is contained in:
Alexander Korotkov
2019-09-19 21:30:19 +03:00
parent 0a97edb12e
commit 6cae9d2c10
10 changed files with 140 additions and 101 deletions
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16
src/backend/access/gist/gistscan.c
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@ -33,26 +33,23 @@ pairingheap_GISTSearchItem_cmp(const pairingheap_node *a, const pairingheap_node
const GISTSearchItem *sb = (const GISTSearchItem *) b;
IndexScanDesc scan = (IndexScanDesc) arg;
int i;
double *da = GISTSearchItemDistanceValues(sa, scan->numberOfOrderBys),
*db = GISTSearchItemDistanceValues(sb, scan->numberOfOrderBys);
bool *na = GISTSearchItemDistanceNulls(sa, scan->numberOfOrderBys),
*nb = GISTSearchItemDistanceNulls(sb, scan->numberOfOrderBys);
/* Order according to distance comparison */
for (i = 0; i < scan->numberOfOrderBys; i++)
{
if (na[i])
if (sa->distances[i].isnull)
{
if (!nb[i])
if (!sb->distances[i].isnull)
return -1;
}
else if (nb[i])
else if (sb->distances[i].isnull)
{
return 1;
}
else
{
int cmp = -float8_cmp_internal(da[i], db[i]);
int cmp = -float8_cmp_internal(sa->distances[i].value,
sb->distances[i].value);
if (cmp != 0)
return cmp;
@ -100,8 +97,7 @@ gistbeginscan(Relation r, int nkeys, int norderbys)
so->queueCxt = giststate->scanCxt; /* see gistrescan */
/* workspaces with size dependent on numberOfOrderBys: */
so->distanceValues = palloc(sizeof(double) * scan->numberOfOrderBys);
so->distanceNulls = palloc(sizeof(bool) * scan->numberOfOrderBys);
so->distances = palloc(sizeof(so->distances[0]) * scan->numberOfOrderBys);
so->qual_ok = true; /* in case there are zero keys */
if (scan->numberOfOrderBys > 0)
{