ddl: fix dynamic parameter adjustment failure in txn and local ingest mode (#63605)

[ti-chi-bot]

This is an automated cherry-pick of #63605

What problem does this PR solve?

Issue Number: close #63201

Problem Summary:
After #60828, the runReorgJob will return periodically, this means every time we enter the runOneJobStep, the Job is a new job, not the one pass to backfill worker, so the config in the initial Job can't be updated.

tidb/pkg/ddl/job_worker.go

Lines 898 to 900 in b3011b6

	job.ReorgMeta.SetConcurrency(latestJob.ReorgMeta.GetConcurrency())
	job.ReorgMeta.SetBatchSize(latestJob.ReorgMeta.GetBatchSize())
	job.ReorgMeta.SetMaxWriteSpeed(latestJob.ReorgMeta.GetMaxWriteSpeed())

What changed and how does it work?

Update config from system table in the adjust config loop.

Check List

Tests

• Unit test
• Integration test
  After this pr, use admin alter ddl jobs can adjust thread batch_size and max_write_speed normally

• 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

[ti-chi-bot]

@fzzf678 This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[ti-chi-bot]

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[fzzf678]

/unhold

[codecov]

Codecov Report

❌ Patch coverage is 73.33333% with 8 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release-8.5@a8777b2). Learn more about missing BASE report.

Additional details and impacted files

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Flag	Coverage Δ
integration	38.2512% <73.3333%> (?)
unit	72.8077% <40.0000%> (?)

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

Components	Coverage Δ
dumpling	52.9278% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	63.2263% <0.0000%> (?)

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[Benjamin2037]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Benjamin2037, fzzf678

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• OWNERS [Benjamin2037]
• pkg/ddl/OWNERS [Benjamin2037]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-09-23 01:07:13.186451639 +0000 UTC m=+318843.256945321: ☑️ agreed by fzzf678.
• 2025-09-23 01:35:48.570144093 +0000 UTC m=+320558.640637774: ☑️ agreed by Benjamin2037.