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Remove obsolete comments about functional dependencies

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Initial submitted versions of the functional dependencies patch ignored
row groups that were smaller than a configured size.  However, that
consideration was removed in late stages of the patch just before
commit, but some comments referring to it remained.  Remove them to
avoid confusion.

Author: Atsushi Torikoshi
Discussion: https://postgr.es/m/7cfb23fc-4493-9c02-5da9-e505fd0115d2@lab.ntt.co.jp
This commit is contained in:
Alvaro Herrera 2017-07-26 11:40:39 -04:00
parent 54dacc7466
commit c28e4f4dc6
2 changed files with 0 additions and 12 deletions
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4
src/backend/statistics/README.dependencies
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@ -71,10 +71,6 @@ To count the rows consistent with the dependency (a => b):
(c) If there's a single distinct value in 'b', the rows are consistent with (c) If there's a single distinct value in 'b', the rows are consistent with
the functional dependency, otherwise they contradict it. the functional dependency, otherwise they contradict it.
The algorithm also requires a minimum size of the group to consider it
consistent (currently 3 rows in the sample). Small groups make it less likely
to break the consistency.
Clause reduction (planner/optimizer) Clause reduction (planner/optimizer)
------------------------------------ ------------------------------------

8
src/backend/statistics/dependencies.c
View File

@ -286,14 +286,6 @@ dependency_degree(int numrows, HeapTuple *rows, int k, AttrNumber *dependency,
* first (k-1) columns. If there's a single value in the last column, we * first (k-1) columns. If there's a single value in the last column, we
* count the group as 'supporting' the functional dependency. Otherwise we * count the group as 'supporting' the functional dependency. Otherwise we
* count it as contradicting. * count it as contradicting.
*
* We also require a group to have a minimum number of rows to be
* considered useful for supporting the dependency. Contradicting groups
* may be of any size, though.
*
* XXX The minimum size requirement makes it impossible to identify case
* when both columns are unique (or nearly unique), and therefore
* trivially functionally dependent.
*/ */
/* start with the first row forming a group */ /* start with the first row forming a group */