planner: Remove an unused return value from cardinality.Selectivity.

[wddevries]

What problem does this PR solve?

Issue Number: close #65899

Problem Summary:

What changed and how does it work?

This pull request removes the second unused return value in cardinality.Selectivity.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.
  • This return value is not used.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[tiprow]

Hi @wddevries. Thanks for your PR.

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[lance6716]

/lgtm

[codecov]

Codecov Report

❌ Patch coverage is 80.76923% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.8380%. Comparing base (245c8e1) to head (94d2ef1).
⚠️ Report is 41 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #65900        +/-   ##
================================================
+ Coverage   77.7927%   77.8380%   +0.0453%     
================================================
  Files          2001       1923        -78     
  Lines        545191     536347      -8844     
================================================
- Hits         424119     417482      -6637     
+ Misses       119410     118835       -575     
+ Partials       1662         30      -1632     

Flag	Coverage Δ
integration	41.9856% <61.5384%> (-6.1839%)	⬇️
unit	76.9336% <76.9230%> (+0.5041%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	56.7974% <ø> (ø)
parser	∅ <ø> (∅)
br	48.8957% <ø> (-12.0781%)	⬇️

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[wddevries]

/retest

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[wddevries]

/test unit-test

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-01-29 04:18:30.847031083 +0000 UTC m=+1245138.460987939: ☑️ agreed by lance6716.
• 2026-02-01 18:53:29.983916165 +0000 UTC m=+33881.085314881: ☑️ agreed by terry1purcell.

[Copilot]

Pull request overview

This PR simplifies the planner/cardinality.Selectivity API by removing its unused second return value and updates all call sites accordingly.

Changes:

• Change cardinality.Selectivity to return only (float64, error) instead of (float64, []*StatsNode, error).
• Update all planner call sites to match the new signature.
• Update benchmarks/tests that called Selectivity to use the new signature.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pkg/planner/cardinality/selectivity.go	Removes the unused []*StatsNode return value from Selectivity and adjusts internal returns accordingly.
pkg/planner/cardinality/selectivity_test.go	Updates benchmark/tests to use the new (float64, error) signature.
pkg/planner/core/stats.go	Updates selectivity derivation call sites to the new signature.
pkg/planner/core/exhaust_physical_plans.go	Updates selectivity estimation calls used during task construction.
pkg/planner/core/find_best_task.go	Updates selectivity estimation calls during plan construction.
pkg/planner/core/indexmerge_path.go	Updates selectivity call for index-merge AND path estimation.
pkg/planner/core/indexmerge_unfinished_path.go	Updates selectivity call for index-merge OR path estimation.
pkg/planner/core/operator/physicalop/physical_table_scan.go	Updates selectivity call used for pushed filter estimation.
pkg/planner/core/operator/physicalop/task.go	Updates selectivity call used for root task condition handling.
pkg/planner/core/operator/physicalop/task_base.go	Updates selectivity call used when converting MPP task to root task.
pkg/planner/core/operator/physicalop/tiflash_predicate_push_down.go	Updates selectivity calls used for TiFlash predicate pushdown heuristics.

Comments suppressed due to low confidence (1)

pkg/planner/core/stats.go:537

• The commented-out block below still references nodes from cardinality.Selectivity, but Selectivity no longer returns stats nodes. Please update/remove that TODO snippet (or adjust it to the new API) to avoid leaving stale, non-actionable guidance in the code.

	selectivity, err := cardinality.Selectivity(ds.SCtx(), ds.TableStats.HistColl, conds, filledPaths)
	if err != nil {
		logutil.BgLogger().Debug("something wrong happened, use the default selectivity", zap.Error(err))
		selectivity = cost.SelectionFactor
	}

[terry1purcell]

/retest-required

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[terry1purcell]

/ok-to-test

[terry1purcell]

/retest-required

[hawkingrei]

/retest

[terry1purcell]

/retest-required

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, lance6716, terry1purcell

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[hawkingrei]

/retest

[hawkingrei]

/retest