statistics: smaller task channel when to merge global stats

[hawkingrei]

What problem does this PR solve?

Issue Number: close #47762

Problem Summary:

What is changed and how it works?

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

[codecov]

Codecov Report

Merging #47761 (42edc82) into master (ac1f0d9) will increase coverage by 0.8938%.
The diff coverage is 100.0000%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #47761        +/-   ##
================================================
+ Coverage   71.8931%   72.7869%   +0.8938%     
================================================
  Files          1398       1421        +23     
  Lines        405200     411575      +6375     
================================================
+ Hits         291311     299573      +8262     
+ Misses        94269      93151      -1118     
+ Partials      19620      18851       -769     

Flag	Coverage Δ
integration	41.3384% <100.0000%> (?)

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

Components	Coverage Δ
dumpling	53.9913% <ø> (ø)
parser	∅ <ø> (∅)
br	48.6682% <ø> (-4.2653%)	⬇️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chrysan, winoros

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• OWNERS [chrysan,winoros]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-10-18 14:29:54.205039275 +0000 UTC m=+1840191.792149412: ☑️ agreed by chrysan.
• 2023-10-18 15:00:46.358181075 +0000 UTC m=+1842043.945291220: ☑️ agreed by winoros.

[tiprow]

@hawkingrei: 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
tiprow_fast_test	42edc82	link	true	/test tiprow_fast_test

Full PR test history. Your PR dashboard.

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[hawkingrei]

/cherrypick release-7.5

[ti-chi-bot]

@hawkingrei: new pull request created to branch release-7.5: #47813.

In response to this:

/cherrypick release-7.5

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