ttl: rollback the scan trasnaction even if the BEGIN failed.

[YangKeao]

What problem does this PR solve?

Issue Number: close #58900

Problem Summary:

Previously, the RunInTxn will only rollback the transaction after the BEGIN runs successfully. However, if the BEGIN is killed after setting the transaction status, it can still leave a valid transaction. We'll need to also ROLLBACK it.

The effect is that when we are cancelling a TTL task (scaling the workers, stepping out of the TTL window, stopping the TTL function...), a session with valid transaction may pollute the session pool.

What changed and how does it work?

Move the defer ... ROLLBACK logic to the top of the RunInTxn function.

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.

Release note

Fix the issue that canceling a TTL task may return a polluted session to global session pool.

[YangKeao]

/check-issue-triage-complete

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.5448%. Comparing base (9c01dcd) to head (0ae413f).
Report is 5 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #58943        +/-   ##
================================================
+ Coverage   73.1695%   73.5448%   +0.3753%     
================================================
  Files          1678       1680         +2     
  Lines        464110     465025       +915     
================================================
+ Hits         339587     342002      +2415     
+ Misses       103656     102143      -1513     
- Partials      20867      20880        +13     

Flag	Coverage Δ
integration	42.8851% <0.0000%> (?)
unit	72.2773% <100.0000%> (-0.0843%)	⬇️

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

Components	Coverage Δ
dumpling	52.6910% <ø> (ø)
parser	∅ <ø> (∅)
br	45.4402% <ø> (-0.2919%)	⬇️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, lcwangchao

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• OWNERS [hawkingrei,lcwangchao]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-01-15 09:20:33.328726669 +0000 UTC m=+110304.783772818: ☑️ agreed by hawkingrei.
• 2025-01-15 09:26:40.238838327 +0000 UTC m=+110671.693884476: ☑️ agreed by lcwangchao.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #58948.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #58949.

[YangKeao]

Wow! It's merged so fast. Amazing.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #58950.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #58951.