ddl: change finishedWritingNeedImport to importStarted

[lance6716]

What problem does this PR solve?

Issue Number: close #53641

Problem Summary:

What changed and how does it work?

in the old code, finishedWritingNeedImport checks closedEngine != nil which stands for "there's a pending engine to be imported". Now it checks openedEngine == nil which stands for "all writing of this engine is finished". The difference is if retry happens after importing engine is finished, closedEngine is assigned to nil, and old finishedWritingNeedImport returns false but importStarted returns true

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]

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[D3Hunter]

/check-issue-triage-complete

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.5592%. Comparing base (afd2343) to head (7470f75).
Report is 2 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #53643        +/-   ##
================================================
+ Coverage   72.5370%   74.5592%   +2.0221%     
================================================
  Files          1506       1506                
  Lines        430741     431163       +422     
================================================
+ Hits         312447     321472      +9025     
+ Misses        98968      89748      -9220     
- Partials      19326      19943       +617     

Flag	Coverage Δ
integration	49.2651% <83.3333%> (?)
unit	71.4332% <50.0000%> (-0.0964%)	⬇️

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

Components	Coverage Δ
dumpling	53.9957% <ø> (ø)
parser	∅ <ø> (∅)
br	50.4708% <ø> (+8.6656%)	⬆️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: D3Hunter, tangenta

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-29 06:34:41.493407237 +0000 UTC m=+2844635.250542810: ☑️ agreed by D3Hunter.
• 2024-05-29 07:26:24.580497977 +0000 UTC m=+2847738.337633551: ☑️ agreed by tangenta.