planner: tighten full-range fast path for index estimation

[terry1purcell]

Two fixes raised in the release-8.5 cherry-pick review (PR #66695) that also apply on master:

1. Move canSkipIndexEstimation ahead of IndexStatsIsInvalid so the full-range fast path short-circuits before IndexStatsIsInvalid queues an unnecessary async histogram load when the index stats are not fully loaded. Guarded by idx != nil so the pseudo fallback is preserved.

2. Reject ranges with LowExclude or HighExclude in isFullRangeIncludingNulls. A range like (NULL, +inf) drops the NULL endpoint and shrinks the result, so it must not trigger the fast path.

Tighten TestCanSkipIndexEstimation to actually exercise these cases: model 10 NULL rows in the index histogram (NullCount=10) so the not-null estimate is strictly below RealtimeCount, switch the assertion to require.Less, and add a case covering (NULL, +inf) with an exclusive lower bound.

What problem does this PR solve?

Issue Number: ref #64791

Problem Summary:

What changed and how does it work?

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.

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

Summary by CodeRabbit

• Bug Fixes

  • Improved cardinality estimation: planner now short-circuits earlier for eligible indexes and correctly rejects ranges with exclusive endpoints, preventing incorrect fast-path use and ensuring counts exclude endpoints like NULL when appropriate.

• Tests

  • Tightened tests and updated plan expectations to verify the fast-path only applies to NULL-inclusive full ranges and async stats-loading behavior.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

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Plan: Pro

Run ID: f68df245-60ae-4eb9-948e-3fac77c54c65

📥 Commits

Reviewing files that changed from the base of the PR and between c13524f and 9452072.

📒 Files selected for processing (1)

• pkg/planner/cardinality/selectivity_test.go

🚧 Files skipped from review as they are similar to previous changes (1)

• pkg/planner/cardinality/selectivity_test.go

---

📝 Walkthrough

Walkthrough

Moves the index-estimation fast-path earlier to return scaled realtime counts for inclusive full-range non-MV/non-partial indexes, tightens full-range NULL-boundary checks to reject exclusive bounds, and updates tests and EXPLAIN expectations to match the new short-circuiting behavior.

Changes

Index Cardinality Estimation

Layer / File(s)	Summary
Fast-path relocation and boundary validation pkg/planner/cardinality/row_count_index.go	GetRowCountByIndexRanges now short-circuits earlier using GetScaledRealtimeAndModifyCnt for qualifying non-MV, non-partial inclusive full-range indexes. isFullRangeIncludingNulls now rejects ranges with exclusive low or high bounds.
Test and EXPLAIN updates pkg/planner/cardinality/selectivity_test.go, pkg/executor/test/analyzetest/analyze_test.go	TestCanSkipIndexEstimation builds mock stats with 50 non-NULL + 10 NULL rows, regenerates index-histogram keys from non-NULL values, and tightens assertions so the fast-path only applies to inclusive [NULL, +inf) ranges (which must return RealtimeCount and not enqueue async loading); other ranges (exclude-NULL, bounded, or exclusive endpoints) must produce estimates strictly less than RealtimeCount. TestAnalyzeMVIndex EXPLAIN expectations updated to show ia:allEvicted and j:unInitialized after async-loading emulation.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Suggested reviewers

• hawkingrei
• AilinKid

Poem

🐰 I hopped through NULLs and bounds so wide,
I nudged the fast-path to the earlier side,
Inclusive ranges now leap, exclusive stay shy,
Tests clap their paws, and explain lets out a sigh,
Carrots for CI—fast counts, no async try!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: tightening the full-range fast path for index estimation in the planner package.
Description check	✅ Passed	The description covers the problem summary, changes made, and test updates. However, the Issue Number section is incomplete with only a 'ref' without the issue number explicitly stated.
Docstring Coverage	✅ Passed	Docstring coverage is 83.33% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[terry1purcell]

/ok-to-test

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.6766%. Comparing base (296420e) to head (9452072).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #68474        +/-   ##
================================================
- Coverage   77.2806%   75.6766%   -1.6040%     
================================================
  Files          2010       2008         -2     
  Lines        555350     563899      +8549     
================================================
- Hits         429178     426740      -2438     
- Misses       125252     137039     +11787     
+ Partials        920        120       -800     

Flag	Coverage Δ
integration	41.5378% <100.0000%> (+1.7448%)	⬆️

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

Components	Coverage Δ
dumpling	60.4679% <ø> (ø)
parser	∅ <ø> (∅)
br	49.9534% <ø> (-13.0557%)	⬇️

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