Lightning: Attempt to return writeTooSlow when we experience write timeout.

[OliverS929]

What problem does this PR solve?

Issue Number: ref https://github.com/pingcap/tidb/issues/61326

Problem Summary:

Manual cherry-pick of #61346.

What changed and how does it work?

Check List

Tests

• [x] 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[bot]]

Hi @OliverS929. Thanks for your PR.

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[OliverS929]

/ok-to-test

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 38.46154% with 32 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-7.5@469af9d). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #61796   +/-   ##
================================================
  Coverage               ?   72.3125%           
================================================
  Files                  ?       1417           
  Lines                  ?     415018           
  Branches               ?          0           
================================================
  Hits                   ?     300110           
  Misses                 ?      94958           
  Partials               ?      19950           

Flag	Coverage Δ
unit	72.3125% <38.4615%> (?)

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

Components	Coverage Δ
dumpling	52.9400% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.5625% <0.0000%> (?)

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[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2025-06-18 07:02:47.385350514 +0000 UTC m=+255220.108529495: :ballot_box_with_check: agreed by Benjamin2037.
• 2025-06-18 07:36:59.347042242 +0000 UTC m=+257272.070221222: :ballot_box_with_check: agreed by D3Hunter.

[OliverS929]

/retest

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: 3pointer, Benjamin2037, D3Hunter

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• ~~br/OWNERS~~ [3pointer]
• ~~br/pkg/lightning/OWNERS~~ [Benjamin2037,D3Hunter]

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