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Commitc28e4f4

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Remove obsolete comments about functional dependencies
Initial submitted versions of the functional dependencies patch ignoredrow groups that were smaller than a configured size. However, thatconsideration was removed in late stages of the patch just beforecommit, but some comments referring to it remained. Remove them toavoid confusion.Author: Atsushi TorikoshiDiscussion:https://postgr.es/m/7cfb23fc-4493-9c02-5da9-e505fd0115d2@lab.ntt.co.jp
1 parent54dacc7 commitc28e4f4

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‎src/backend/statistics/README.dependencies‎

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@@ -71,10 +71,6 @@ To count the rows consistent with the dependency (a => b):
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(c) If there's a single distinct value in 'b', the rows are consistent with
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the functional dependency, otherwise they contradict it.
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The algorithm also requires a minimum size of the group to consider it
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consistent (currently 3 rows in the sample). Small groups make it less likely
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to break the consistency.
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Clause reduction (planner/optimizer)
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------------------------------------

‎src/backend/statistics/dependencies.c‎

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

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