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Fix behavior of ~> (cube, int) operator

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~> (cube, int) operator was especially designed for knn-gist search.
However, it appears that knn-gist search can't work correctly with current
behavior of this operator when dataset contains cubes of variable
dimensionality. In this case, the same value of second operator argument
can point to different dimension depending on dimensionality of particular cube.
Such behavior is incompatible with gist indexing of cubes, and knn-gist doesn't
work correctly for it.

This patch changes behavior of ~> (cube, int) operator by introducing dimension
numbering where value of second argument unambiguously identifies number of
dimension. With new behavior, this operator can be correctly supported by
knn-gist. Relevant changes to cube operator class are also included.

Backpatch to v9.6 where operator was introduced.

Since behavior of ~> (cube, int) operator is changed, depending entities
must be refreshed after upgrade. Such as, expression indexes using this
operator must be reindexed, materialized views must be rebuilt, stored
procedures and client code must be revised to correctly use new behavior.
That should be mentioned in release notes.

Noticed by: Tomas Vondra
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 14:42:16 +03:00
parent 08adf688f3
commit b8279a783d
5 changed files with 511 additions and 285 deletions
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9
doc/src/sgml/cube.sgml
View File

@ -186,10 +186,11 @@
<entry><literal>a ~&gt; n</></entry>
<entry><type>float8</></entry>
<entry>
Get <replaceable>n</>-th coordinate in <quote>normalized</> cube
representation, in which the coordinates have been rearranged into
the form <quote>lower left &mdash; upper right</>; that is, the
smaller endpoint along each dimension appears first.
Get <replaceable>n</>-th coordinate of cube in following way:
n = 2 * k - 1 means lower bound of <replaceable>k</>-th
dimension, n = 2 * k means upper bound of
<replaceable>k</>-th dimension. This operator is designed
for KNN-GiST support.
</entry>
</row>