session: fix initGlobalVariableIfNotExists function forget call rs.close

[Defined2014]

What problem does this PR solve?

Issue Number: close #61884

Problem Summary:

What changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Modified v7.5.6 and let it create a mysql.global_variables table with clustered index.

Run v8.5.2 to upgrade the cluster, before this PR, it will failed. After this PR, cluster start up success.

• 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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[LGTM Timeline notifier]

Timeline:

• 2025-06-20 09:21:49.399254406 +0000 UTC m=+436362.122433387: ☑️ agreed by xhebox.
• 2025-06-20 09:23:49.899851178 +0000 UTC m=+436482.623030161: ☑️ agreed by glorv.

[tiprow]

@Defined2014: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
tidb_parser_test	d79b426	link	true	/test tidb_parser_test
fast_test_tiprow	d79b426	link	true	/test fast_test_tiprow

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.5039%. Comparing base (cbafb78) to head (232a50c).
Report is 4 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #61890        +/-   ##
================================================
+ Coverage   73.0325%   73.5039%   +0.4714%     
================================================
  Files          1735       1735                
  Lines        481432     481446        +14     
================================================
+ Hits         351602     353882      +2280     
+ Misses       108298     106060      -2238     
+ Partials      21532      21504        -28     

Flag	Coverage Δ
integration	42.3445% <0.0000%> (?)
unit	72.3556% <100.0000%> (+0.0881%)	⬆️

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Components	Coverage Δ
dumpling	52.7804% <ø> (ø)
parser	∅ <ø> (∅)
br	46.5910% <ø> (+0.0208%)	⬆️

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[Defined2014]

/retest

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[Defined2014]

/retest

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[lance6716]

maybe it's better to use

tidb/pkg/util/sqlexec/restricted_sql_executor.go

Lines 255 to 256 in cbafb78

	// DrainRecordSetAndClose fetches the rows in the RecordSet and closes it.
	func DrainRecordSetAndClose(ctx context.Context, rs RecordSet, maxChunkSize int) ([]chunk.Row, error) {

[Defined2014]

Upated it with sqlexec.ExecSQL

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: glorv, xhebox, yudongusa

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #61905.
But this PR has conflicts, please resolve them!