Planner: Do not allow cardinality to go below 1 | tidb-test=pr/2376

[terry1purcell]

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

[ti-chi-bot]

Hi @terry1purcell. Thanks for your PR.

I'm waiting for a pingcap member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[tiprow]

Hi @terry1purcell. Thanks for your PR.

PRs from untrusted users cannot be marked as trusted with /ok-to-test in this repo meaning untrusted PR authors can never trigger tests themselves. Collaborators can still trigger tests on the PR using /test all.

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[hawkingrei]

/ok-to-test

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.8117%. Comparing base (bab3667) to head (5dd856b).
Report is 1128 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #55242        +/-   ##
================================================
+ Coverage   74.9822%   75.8117%   +0.8295%     
================================================
  Files          1576       1608        +32     
  Lines        365580     463391     +97811     
================================================
+ Hits         274120     351305     +77185     
- Misses        71731      91347     +19616     
- Partials      19729      20739      +1010     

Flag	Coverage Δ
integration	52.0432% <100.0000%> (?)
unit	72.9690% <72.7272%> (-1.0139%)	⬇️

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

Components	Coverage Δ
dumpling	52.9567% <ø> (-2.2327%)	⬇️
parser	∅ <ø> (∅)
br	53.4677% <ø> (+5.6493%)	⬆️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cfzjywxk, qw4990, Rustin170506

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [Rustin170506,cfzjywxk,qw4990]
• pkg/planner/OWNERS [qw4990]
• pkg/statistics/OWNERS [qw4990]
• pkg/table/OWNERS [cfzjywxk]

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]

[LGTM Timeline notifier]

Timeline:

• 2024-08-20 08:42:29.016761824 +0000 UTC m=+254944.151211947: ☑️ agreed by qw4990.
• 2024-08-20 09:25:02.677164186 +0000 UTC m=+257497.811614308: ☑️ agreed by cfzjywxk.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #57217.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #58150.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #58173.

[hawkingrei]

/cherrypick release-7.5

[ti-chi-bot]

@hawkingrei: new pull request could not be created: failed to create pull request against pingcap/tidb#release-7.5 from head ti-chi-bot:cherry-pick-55242-to-release-7.5: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-55242-to-release-7.5."}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request","status":"422"}

In response to this:

/cherrypick release-7.5

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #59074.