restore: use a limited workpool (#51872)

[ti-chi-bot]

This is an automated cherry-pick of #51872

What problem does this PR solve?

Issue Number: ref #50701 close #51621

Problem Summary:
Currently eg.Go will generate too many goroutines if ingest too slow. then it will block goroutine release. eventually consume too many memory or even OOM.

What changed and how does it work?

This PR tried to give a high limitation of total download goroutines. which consider the balance of restore speed and memory usage.

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

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• br/OWNERS [BornChanger,Leavrth]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-03-26 09:49:41.856088777 +0000 UTC m=+1975008.878335165: ☑️ agreed by Leavrth.
• 2024-03-26 09:50:06.855910223 +0000 UTC m=+1975033.878156606: ☑️ agreed by BornChanger.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-8.0@99e63f1). Click here to learn what that means.
The diff coverage is 15.3846%.

Additional details and impacted files

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##             release-8.0     #52110   +/-   ##
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Flag	Coverage Δ
unit	70.4468% <15.3846%> (?)

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

Components	Coverage Δ
dumpling	53.9957% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	45.8072% <0.0000%> (?)