[BugFix] remove load job after db had been dropped

[luohaha]

Why I'm doing:

After dropping the database, the load jobs in the Load Manager were not cleared. This causes the system to frequently print error logs when querying the system table loads :

Get transaction xxx in db xxx failed. msg: databaseTransactionMgr[xxx] does not exist

What I'm doing:

This pull request introduces a new mechanism to clean up load jobs associated with a database when the database is erased. The main changes add a method to remove all load jobs for a given database, integrate it into the database deletion workflow, and provide comprehensive unit tests for this functionality.

Load Job Cleanup Improvements:

• Added a new removeLoadJobsByDb(long dbId) method to the LoadMgr class to remove all load jobs belonging to a specified database, ensuring proper locking and cleanup.
• Updated the LocalMetastore.onEraseDatabase(long dbId) method to call removeLoadJobsByDb, so that all load jobs are removed when a database is erased.

Testing Enhancements:

• Added a new unit test testRemoveLoadJobsByDb in LoadMgrTest.java to verify that load jobs are correctly removed for a given database, including checks for multiple databases and job states.

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
  • This pr needs auto generate documentation
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 4.0
  • 3.5
  • 3.4
  • 3.3

---

Note

Ensures load jobs tied to a database are purged when the database is erased.

• Adds LoadMgr.removeLoadJobsByDb(long dbId) to remove all jobs for a DB under write lock using unprotectedRemoveJobReleatedMeta
• Hooks cleanup into LocalMetastore.onEraseDatabase after removing the DB transaction manager
• Adds LoadMgrTest.testRemoveLoadJobsByDb to verify per-DB job removal and internal map cleanup

^{Written by Cursor Bugbot for commit 32dbf7c. This will update automatically on new commits. Configure here.}

[alvin-celerdata]

@cursor review

[cursor]

✅ Bugbot reviewed your changes and found no bugs!

[sonarqubecloud]

Quality Gate passed

Issues
8 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

[Java-Extensions Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[github-actions]

[FE Incremental Coverage Report]

✅ pass : 11 / 11 (100.00%)

file detail

	path	covered_line	new_line	coverage	not_covered_line_detail
🔵	com/starrocks/server/LocalMetastore.java	1	1	100.00%	[]
🔵	com/starrocks/load/loadv2/LoadMgr.java	10	10	100.00%	[]

[github-actions]

[BE Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[alvin-celerdata]

@cursor review

[cursor]

✅ Bugbot reviewed your changes and found no bugs!