planner: Fix bug in the plan cache when the metadata lock is disabled. (#64795)

[ti-chi-bot]

This is an automated cherry-pick of #64795

What problem does this PR solve?

Issue Number: close #64351

Problem Summary:

When global.tidb_enable_metadata_lock is set to off, the StatementContext.MDLRelatedTableIDs field is not populated. This field is used to populate the tbls and dbNames fields in PlanCacheStmt object, and as a result, the StatementContext.TblInfo2UnionScan field is not populated, which may result in the plan cache returning the incorrect plan.

What changed and how does it work?

MDLRelatedTableIDs is only used to setup PlanCacheStmt, so this patch:

• renames MDLRelatedTableIDs to RelatedTableIDs,
• changes tryLockMDLAndUpdateSchemaIfNecessary to always add the table id to RelatedTableIDs,
• and adds a test for the issue.

Check List

Tests

• [x] 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

[ti-chi-bot]

@wddevries This PR has conflicts, I have hold it. Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[ti-chi-bot[bot]]

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[EmmaDuDu]

/retest

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :warning: Please upload report for BASE (release-8.5@7c29611). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #64965   +/-   ##
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  Hits                   ?     366534           
  Misses                 ?      85775           
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Flag	Coverage Δ
integration	51.7132% <100.0000%> (?)
unit	72.1260% <100.0000%> (?)

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

Components	Coverage Δ
dumpling	52.9278% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	65.6047% <0.0000%> (?)

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[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qw4990, terry1purcell

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Needs approval from an approver in each of these files:

• ~~OWNERS~~ [qw4990]
• ~~pkg/planner/OWNERS~~ [qw4990,terry1purcell]

Approvers can indicate their approval by writing /approve in a comment Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2025-12-14 23:11:20.988992932 +0000 UTC m=+1428225.802770494: :ballot_box_with_check: agreed by terry1purcell.
• 2025-12-15 06:17:46.140866695 +0000 UTC m=+1453810.954644257: :ballot_box_with_check: agreed by qw4990.

[qw4990]

/unhold