executor: do not acqurie pessimistic lock for non-unique index keys (#36229)

[ti-srebot]

cherry-pick #36229 to release-5.0
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/36554

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---

Signed-off-by: ekexium [email protected]

What problem does this PR solve?

Issue Number: close #36235

Problem Summary:

Fix the condition of checking if the index KV is unique or not.

What is changed and how it works?

Check List

Tests

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

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.

bugfix: do not acquire pessimistic lock for non-unique index keys

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• tiancaiamao

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[ti-chi-bot]

@ti-srebot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-srebot]

/run-all-tests

[ti-srebot]

@ekexium you're already a collaborator in bot's repo.

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/3fb3036de08a158d123b5af8af92af2d8e07c8b3

[VelocityLight]

This pull request is closed because it's related version has closed automatic cherry-picking.
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