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llow negative coordinate for ~> (cube, int) operator

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~> (cube, int) operator was especially designed for knn-gist search.
However, knn-gist supports only ascending ordering of results. Nevertheless
it would be useful to support descending ordering by ~> (cube, int) operator.
We provide workaround for that: negative coordinate give us inversed value
of corresponding cube bound. Therefore, knn search using negative coordinate
gives us an effect of descending ordering by cube bound.

Author: Alexander Korotkov
Reviewed by: Tomas Vondra, Andrey Borodin
Discussion: https://www.postgresql.org/message-id/flat/a9657f6a-b497-36ff-e56-482a2c7e3292@2ndquadrant.com
This commit is contained in:
Teodor Sigaev
2018-01-11 14:49:36 +03:00
parent 563a053bdd
commit f50c80dbb1
5 changed files with 379 additions and 14 deletions
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44
contrib/cube/cube.c
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@ -1343,12 +1343,20 @@ g_cube_distance(PG_FUNCTION_ARGS)
*/
int coord = PG_GETARG_INT32(1);
bool isLeaf = GistPageIsLeaf(entry->page);
bool inverse = false;
/* 0 is the only unsupported coordinate value */
if (coord <= 0)
if (coord == 0)
ereport(ERROR,
(errcode(ERRCODE_ARRAY_ELEMENT_ERROR),
errmsg("cube index %d is out of bounds", coord)));
errmsg("zero cube index is not defined")));
/* Return inversed value for negative coordinate */
if (coord < 0)
{
coord = -coord;
inverse = true;
}
if (coord <= 2 * DIM(cube))
{
@ -1376,9 +1384,14 @@ g_cube_distance(PG_FUNCTION_ARGS)
/*
* For non-leaf we should always return lower bound,
* because even upper bound of a child in the subtree can
* be as small as our lower bound.
* be as small as our lower bound. For inversed case we
* return upper bound because it becomes lower bound for
* inversed value.
*/
retval = Min(cube->x[index], cube->x[index + DIM(cube)]);
if (!inverse)
retval = Min(cube->x[index], cube->x[index + DIM(cube)]);
else
retval = Max(cube->x[index], cube->x[index + DIM(cube)]);
}
}
}
@ -1386,6 +1399,10 @@ g_cube_distance(PG_FUNCTION_ARGS)
{
retval = 0.0;
}
/* Inverse return value if needed */
if (inverse)
retval = -retval;
}
else
{
@ -1542,11 +1559,15 @@ cube_coord(PG_FUNCTION_ARGS)
* getter. Moreover, indexed dataset may contain cubes of different dimensions
* number. Accordingly, this coordinate getter should be able to return
* lower/upper bound for particular dimension independently on number of cube
* dimensions.
* dimensions. Also, KNN-GiST supports only ascending sorting. In order to
* support descending sorting, this function returns inverse of value when
* negative coordinate is given.
*
* Long story short, this function uses following meaning of coordinates:
* # (2 * N - 1) -- lower bound of Nth dimension,
* # (2 * N) -- upper bound of Nth dimension.
* # (2 * N) -- upper bound of Nth dimension,
* # - (2 * N - 1) -- negative of lower bound of Nth dimension,
* # - (2 * N) -- negative of upper bound of Nth dimension.
*
* When given coordinate exceeds number of cube dimensions, then 0 returned
* (reproducing logic of GiST indexing of variable-length cubes).
@ -1560,10 +1581,17 @@ cube_coord_llur(PG_FUNCTION_ARGS)
float8 result;
/* 0 is the only unsupported coordinate value */
if (coord <= 0)
if (coord == 0)
ereport(ERROR,
(errcode(ERRCODE_ARRAY_ELEMENT_ERROR),
errmsg("cube index %d is out of bounds", coord)));
errmsg("zero cube index is not defined")));
/* Return inversed value for negative coordinate */
if (coord < 0)
{
coord = -coord;
inverse = true;
}
if (coord <= 2 * DIM(cube))
{