br: allow append migration to work with restore

[Tristan1900]

What problem does this PR solve?

Issue Number: close #62546

Problem Summary:

What changed and how does it work?

change append migration op to acquire read lock instead of write lock so it can works with restore at the same time.
create a new append_lock that append will acquire after acquiring read lock (two phase locking), to prevent multiple append threads to race.

Append migration should work fine with restore as new ssts added will have larger TS that any restore should filter out, effectively invisible to the ongoing restore.

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

[tiprow]

Hi @Tristan1900. Thanks for your PR.

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[codecov]

Codecov Report

❌ Patch coverage is 64.17910% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.1980%. Comparing base (833b1be) to head (f2b7ebb).
⚠️ Report is 143 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #62433        +/-   ##
================================================
+ Coverage   72.8992%   77.1980%   +4.2987%     
================================================
  Files          1753       1818        +65     
  Lines        484943     524477     +39534     
================================================
+ Hits         353520     404886     +51366     
+ Misses       109785      96720     -13065     
- Partials      21638      22871      +1233     

Flag	Coverage Δ
integration	50.7450% <49.2537%> (?)
unit	74.5196% <41.7910%> (+2.3751%)	⬆️

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

Components	Coverage Δ
dumpling	52.9532% <ø> (+0.1728%)	⬆️
parser	∅ <ø> (∅)
br	63.7811% <64.1791%> (+17.4794%)	⬆️

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[Tristan1900]

/retest

[tiprow]

@Tristan1900: 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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[Tristan1900]

/retest

[tiprow]

@Tristan1900: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/retest

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[Tristan1900]

/retest

[tiprow]

@Tristan1900: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/retest

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Leavrth, YuJuncen

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Needs approval from an approver in each of these files:

• br/OWNERS [Leavrth,YuJuncen]
• br/pkg/storage/OWNERS [Leavrth,YuJuncen]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-07-31 10:02:50.868347294 +0000 UTC m=+171983.553617530: ☑️ agreed by YuJuncen.
• 2025-08-01 03:04:01.108892569 +0000 UTC m=+233253.794162805: ☑️ agreed by Leavrth.

[tiprow]

@Tristan1900: 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
tidb_parser_test	f2b7ebb	link	true	/test tidb_parser_test

Full PR test history. Your PR dashboard.

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.