topsql: move fast plan check to beginning of observeStmtBeginForTopSQL when disable top sql (#60605)

[ti-chi-bot]

This is an automated cherry-pick of #60605

What problem does this PR solve?

Issue Number: close #60604

Problem Summary: see #60604

What changed and how does it work?

The fast plan check is now performed at the very beginning of observeStmtBeginForTopSQL. This change skips the expensive GetPlanDigest call when TopSQL is disabled and the execution plan is a fast path, since point gets return early and the plan digest is only cached without further use.

For this optimization to take effect, TopSQL, slow log, and statement summary must be disabled.

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.

before:

after (no GetPlanDigest found in flame graph):

in our special edition of TiDB, sysbench point select QPS can have 2~3% increment

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]

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.

To merge this cherry pick:

1. It must be approved by the approvers firstly.
2. AFTER it has been approved by approvers, please wait for the cherry-pick merging approval from triage owners.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (release-8.5@ca939b3). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #60607   +/-   ##
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  Coverage               ?   36.8461%           
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  Files                  ?       1675           
  Lines                  ?     612840           
  Branches               ?          0           
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  Hits                   ?     225808           
  Misses                 ?     364871           
  Partials               ?      22161           

Flag	Coverage Δ
integration	36.8461% <100.0000%> (?)

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Components	Coverage Δ
dumpling	∅ <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	23.1151% <0.0000%> (?)

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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	4fcd8b6	link	true	/test unit-test
idc-jenkins-ci-tidb/check_dev_2	4fcd8b6	link	true	/test check-dev2

Full PR test history. Your PR dashboard.

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lance6716

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Details

Needs approval from an approver in each of these files:

• OWNERS [lance6716]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-04-17 04:53:59.448549448 +0000 UTC m=+2923333.132785544: ☑️ agreed by lance6716.

[tiprow]

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

Test name	Commit	Details	Required	Rerun command
fast_test_tiprow	4fcd8b6	link	true	/test fast_test_tiprow_for_release

Full PR test history. Your PR dashboard.

Details

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 kubernetes-sigs/prow repository. I understand the commands that are listed here.