Planner: Do not allow cardinality to go below 1 | tidb-test=pr/2450

[ti-chi-bot]

This is an automated cherry-pick of #55242

What problem does this PR solve?

Issue Number: close #47400

Problem Summary:

What changed and how does it work?

Ensure that the cardinality estimate does not go below 1. As the estimate approaches zero, then all plans are inexpensive which makes it difficult for the optimizer to differentiate the plan choices.

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

[terry1purcell]

/retest

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-12-12 09:41:29.420852605 +0000 UTC m=+517879.509655145: ☑️ agreed by hawkingrei.

[terry1purcell]

/retest

[hawkingrei]

/retest

[hawkingrei]

@terry1purcell You have test results that are not updated. The deadline is approaching, please process it as soon as possible

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: hawkingrei
Once this PR has been reviewed and has the lgtm label, please assign zimulala for approval. For more information see the Code Review Process.

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Needs approval from an approver in each of these files:

• OWNERS [hawkingrei]
• pkg/planner/OWNERS [hawkingrei]
• pkg/statistics/OWNERS [hawkingrei]
• pkg/table/OWNERS

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[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-chi-bot]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/unit-test	bf2b5ce	link	true	/test unit-test
idc-jenkins-ci-tidb/check_dev_2	bf2b5ce	link	true	/test check-dev2
idc-jenkins-ci-tidb/mysql-test	bf2b5ce	link	true	/test mysql-test
idc-jenkins-ci-tidb/check_dev	bf2b5ce	link	true	/test check-dev
idc-jenkins-ci-tidb/build	bf2b5ce	link	true	/test build

Full PR test history. Your PR dashboard.

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