disttask: dynamic dispatch subtasks

[ywqzzy]

What problem does this PR solve?

Issue Number: ref #46258

Problem Summary:
In previous implementation, we batch all subtasks in one txn to submit subtasks.
It's possible that all subtasks are big then the size will up to txn limit.
And generating all subtasks will be slow, which will make some tidb workers idle.

What is changed and how it works?

Generate and dispatch subtasks in multiple txns.
In DispatcherExt, add the following 2 intefaces:

1. Finished(task *proto.Task) bool: When return true, mark the task as succeed.
2. StageFinished(task *proto.Task) bool: When return true, update the task step++.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

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]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[tiprow]

Hi @ywqzzy. Thanks for your PR.

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[codecov]

Codecov Report

Merging #46593 (851a802) into master (4716f1b) will decrease coverage by 0.9174%.
The diff coverage is 43.3121%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #46593        +/-   ##
================================================
- Coverage   73.3585%   72.4411%   -0.9174%     
================================================
  Files          1327       1348        +21     
  Lines        396878     405685      +8807     
================================================
+ Hits         291144     293883      +2739     
- Misses        87170      93076      +5906     
- Partials      18564      18726       +162     

Flag	Coverage Δ
integration	27.7598% <0.0000%> (?)

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

Components	Coverage Δ
dumpling	54.0444% <ø> (ø)
parser	84.9884% <ø> (-0.0135%)	⬇️
br	48.1946% <ø> (-4.5847%)	⬇️

[ywqzzy]

I will remove the EnableDynamicDispatch column

[ywqzzy]

/cc @wjhuang2016

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Benjamin2037, wjhuang2016

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-09-08 10:11:25.691103795 +0000 UTC m=+4867.615660189: ☑️ agreed by Benjamin2037.
• 2023-09-11 07:26:28.741965422 +0000 UTC m=+254170.666521816: ☑️ agreed by wjhuang2016.

[ywqzzy]

/retest

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@ywqzzy: 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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[hawkingrei]

/ok-to-test

[ywqzzy]

/retest

[tiprow]

@ywqzzy: 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
tiprow_fast_test	851a802	link	true	/test tiprow_fast_test

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