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

Commits on Mar 26, 2025

  1. Improve group number estimation. 

    Estimating GROUP BY x optimisation employs a distinct statistic for column x.
But if we have an expression like 'x=y' somewhere down the query tree, the
number of different values can't be more than the smaller distinct value on
columns 'x' and 'y'. That means it is possible to correct the estimation with
knowledge provided by the equivalence class.

In this commit, the estimate_num_groups routine is changed to include PathKey
nodes in the presortedExprs list. With the PathKey node, we can pass through
its equivalence class members and correct the distinct estimation.

To avoid multiple calls on statistic tuples, the em_ndistinct cache field
is introduced.
    @danolivo
    danolivo authored and Commitfest Bot committed Mar 26, 2025
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  2. [CF 5093] Incremental Sort Cost Estimation Instability 

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

https://commitfest.postgresql.org/patch/5093

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/[email protected]
Author(s): Andrei Lepikhov
    Commitfest Bot committed Mar 26, 2025
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