tables: force to lock the touched index in DML when DDL merging temp index (#62387)

[ti-chi-bot]

This is an automated cherry-pick of #62387

What problem does this PR solve?

Issue Number: close #62337

Problem Summary:

see descriptions in issue. We choose the second way to fix it.

What changed and how does it work?

When the index is in state BackfillStateReadyToMerge or BackfillStateMerging, we also lock the touched non-unique indices to ensure the correctness, even if the DDL does not lock the row.

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

[ti-chi-bot]

@lcwangchao 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]

@ti-chi-bot: ## If you want to know how to resolve it, please read the guide in TiDB Dev Guide.

Details

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[lcwangchao]

/unhold

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-8.5@3098ba5). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #62400   +/-   ##
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  Hits                   ?     363964           
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Flag	Coverage Δ
integration	37.4521% <100.0000%> (?)
unit	73.0609% <100.0000%> (?)

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Components	Coverage Δ
dumpling	52.9278% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	52.7007% <0.0000%> (?)

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[Benjamin2037]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Benjamin2037, lcwangchao

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Details

Needs approval from an approver in each of these files:

• OWNERS [Benjamin2037,lcwangchao]
• pkg/table/OWNERS [Benjamin2037]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-07-15 03:47:34.563949632 +0000 UTC m=+2576307.287128611: ☑️ agreed by Benjamin2037.
• 2025-07-15 05:55:37.82856139 +0000 UTC m=+2583990.551740372: ☑️ agreed by lcwangchao.