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base repository: postgresql-cfbot/postgresql
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  • 2 commits
  • 5 files changed
  • 2 contributors

Commits on Mar 9, 2025

  1. Use extended stats for precise estimation of bucket size in hash join 

    Recognizing the real-life complexity where columns in the table often have
functional dependencies, PostgreSQL's estimation of the number of distinct
values over a set of columns can be underestimated (or much rarely,
overestimated) when dealing with multi-clause JOIN.  In the case of hash
join, it can end up with a small number of predicted hash  buckets and, as
a result, picking non-optimal merge join.

To improve the situation, we introduce one additional stage of bucket size
estimation - having two or more join clauses estimator lookup for extended
statistics and use it for multicolumn estimation.  Clauses are grouped into
lists, each containing expressions referencing the same relation.  The result
of the multicolumn estimation made over such a list is combined with others
according to the caller's logic.  Clauses that are not estimated are returned
to the caller for further estimation.

Discussion: https://postgr.es/m/52257607-57f6-850d-399a-ec33a654457b%40postgrespro.ru
Author: Andrei Lepikhov <[email protected]>
Reviewed-by: Andy Fan <[email protected]>
Reviewed-by: Tomas Vondra <[email protected]>
Reviewed-by: Alena Rybakina <[email protected]>
Reviewed-by: Alexander Korotkov <[email protected]>
    @akorotkov
    akorotkov authored and Commitfest Bot committed Mar 9, 2025
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  2. [CF 5114] v3 - MergeJoin beats HashJoin in the case of multiple hash … 

    …clauses

This branch was automatically generated by a robot using patches from an
email thread registered at:

https://commitfest.postgresql.org/patch/5114

The branch will be overwritten each time a new patch version is posted to
the thread, and also periodically to check for bitrot caused by changes
on the master branch.

Patch(es): https://www.postgresql.org/message-id/CAPpHfdsTnnya8zCAjzTf8Ytw9=4au3o_8WmVpGK-Zn35fSXcyg@mail.gmail.com
Author(s): Andrei Lepikhov
    Commitfest Bot committed Mar 9, 2025
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