ddl: decouple job seq number from job history & reset its allocator on owner change

[D3Hunter]

What problem does this PR solve?

Issue Number: ref #54436

Problem Summary:

What changed and how does it work?

as title

• currently, SeqNum is used to identify the order of moving the job into DDL history, it's not the order of the job execution. for jobs with dependency, or if they are run in the same session, their SeqNum will be in increasing order. when using fast create table, there might duplicate seq_num as any TiDB can execute the DDL in this case.
• after this PR, the SeqNum will always start from 1 when DDL owner not changed, and for jobs with dependency, or if they are run in the same session, their SeqNum will be in increasing order is still maintained. on owner change, new owner will reset and start it from 1 again. as previous semantic forces 'moving jobs into DDL history' part to be serial, it's more complex and has very limited usage scenario, it only used in test right now as far as we know
• the speed of general DDL is not affected by this PR after test, maybe the bottleneck has transfered to job scheduler part after all the optimization we have done.

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 @D3Hunter. Thanks for your PR.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.6868%. Comparing base (d7edc1e) to head (3ed5017).
Report is 28 commits behind head on master.

Additional details and impacted files

@@                Coverage Diff                @@
##             master     #54774         +/-   ##
=================================================
- Coverage   74.6604%   56.6868%   -17.9737%     
=================================================
  Files          1552       1681        +129     
  Lines        362946     618149     +255203     
=================================================
+ Hits         270977     350409      +79432     
- Misses        72336     244322     +171986     
- Partials      19633      23418       +3785     

Flag	Coverage Δ
integration	37.2586% <80.0000%> (?)
unit	72.3078% <100.0000%> (-1.2742%)	⬇️

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Components	Coverage Δ
dumpling	52.9656% <ø> (-2.2339%)	⬇️
parser	∅ <ø> (∅)
br	52.5950% <ø> (+4.9277%)	⬆️

[D3Hunter]

/retest

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/retest

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-07-22 04:29:38.623364372 +0000 UTC m=+846600.614305835: ☑️ agreed by wjhuang2016.
• 2024-07-23 03:35:27.49498601 +0000 UTC m=+929749.485927480: ☑️ agreed by lance6716.

[D3Hunter]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: D3Hunter, lance6716, wjhuang2016

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• pkg/ddl/OWNERS [wjhuang2016]
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