domain: batch handle the privilege reload event

[tiancaiamao]

What problem does this PR solve?

Issue Number: close #59400

Problem Summary:

After a NotifyPrivilegeUpdate(), the notification from etcd is laggy.

When we're in a batch of privilege modification operations, the laggy event cause that even when the workload is done,
tidb still have a long period of time handling the laggy events.
This use 100% cpu (1 core) even there are no other events.

What changed and how does it work?

Wait for a while to get a batch of the laggy events, handle them together.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Before:

After:

As you can see, after the workload finish, the CPU drop to 0 immediately with this commit.

• 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

[tiprow]

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[codecov]

Codecov Report

Attention: Patch coverage is 36.00000% with 16 lines in your changes missing coverage. Please review.

Project coverage is 74.8454%. Comparing base (e6b4d95) to head (cfee950).
Report is 4 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #59934        +/-   ##
================================================
+ Coverage   72.9252%   74.8454%   +1.9202%     
================================================
  Files          1701       1748        +47     
  Lines        469722     478399      +8677     
================================================
+ Hits         342546     358060     +15514     
+ Misses       106059      97756      -8303     
- Partials      21117      22583      +1466     

Flag	Coverage Δ
integration	48.8213% <36.0000%> (?)
unit	72.2377% <36.0000%> (+0.1012%)	⬆️

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

Components	Coverage Δ
dumpling	52.6910% <ø> (ø)
parser	∅ <ø> (∅)
br	61.4022% <ø> (+16.5718%)	⬆️

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[Defined2014]

Does 1024 here means maxBatchSize? Maybe use a const is more reasonable.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Defined2014
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-03-06 03:42:19.67105816 +0000 UTC m=+499452.799977903: ☑️ agreed by Defined2014.

[tiancaiamao]

/retest

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In response to this:

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[tiancaiamao]

/retest

[tiprow]

@tiancaiamao: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

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/retest

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