ddl: Exchange part schema load fix

[mjonss]

What problem does this PR solve?

Issue Number: ref #46125 close #45791

Problem Summary:

What is changed and how it works?

Check List

Tests

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

Manual test:
Build this PR and use it for starting a cluster tiup playground --db.binpath ./bin/tidb-server
and then run tiflash test sh run-test.sh fullstack-test2/ddl/alter_exchange_partition.test which no longer fails
Also check the tidb.log that there are no failures loading new schema diffs, so no full schema reloads are needed.

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

(Unless 7.4 get released without this fix).

[tiprow]

Hi @mjonss. Thanks for your PR.

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[codecov]

Codecov Report

Merging #46126 (8af8ff1) into master (3846e80) will decrease coverage by 2.0921%.
Report is 15 commits behind head on master.
The diff coverage is 75.7575%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #46126        +/-   ##
================================================
- Coverage   74.7667%   72.6746%   -2.0921%     
================================================
  Files          1292       1304        +12     
  Lines        398141     400460      +2319     
================================================
- Hits         297677     291033      -6644     
- Misses        81100      90938      +9838     
+ Partials      19364      18489       -875     

Flag	Coverage Δ
integration	25.5845% <1.5151%> (-20.6784%)	⬇️
unit	73.3550% <75.7575%> (+0.0028%)	⬆️

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

Components	Coverage Δ
dumpling	54.0444% <ø> (ø)
parser	85.0656% <ø> (ø)
br	47.7384% <ø> (-16.7741%)	⬇️

[mjonss]

/test check-issue-triage-complete

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[tiprow]

@mjonss: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

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[bb7133]

�LGTM

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bb7133, tiancaiamao

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-08-17 01:42:31.493610442 +0000 UTC m=+768116.042626414: ☑️ agreed by tiancaiamao.
• 2023-08-17 10:32:06.908016391 +0000 UTC m=+799891.457032377: ☑️ agreed by bb7133.

[bb7133]

/merge

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #46191.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #46193.