tidb-x: add statement summary system variables (#23001)

[ti-chi-bot]

This is an automated cherry-pick of #23001

What is changed

This PR is translated from: pingcap/docs-cn#21694

Add English documentation for two statement summary system variables, corresponding to pingcap/docs-cn#21694:

• tidb_stmt_summary_group_by_user
• tidb_stmt_summary_persist_evicted

Updated files:

• statement-summary-tables.md
• system-variables.md
• system-variable-reference.md

Check List

Tests:

• ./scripts/markdownlint statement-summary-tables.md system-variable-reference.md system-variables.md
• git diff --check -- statement-summary-tables.md system-variable-reference.md system-variables.md

Summary by CodeRabbit

• Documentation
  • Added TiDB Cloud documentation for two global Boolean system variables.
  • Documented statement summary grouping by executing user, including availability, defaults, and summary reset behavior.
  • Documented persistence of evicted statement summaries, including availability, defaults, and history-query behavior.

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 06a8e1a and ddd649d.

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• system-variables.md

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📝 Walkthrough

Walkthrough

The documentation adds TiDB Cloud behavior details for two GLOBAL Boolean statement-summary variables, including support restrictions, defaults, aggregation behavior, persistence behavior, and history-query effects.

Changes

Statement Summary Variables

Layer / File(s)	Summary
Variable behavior documentation system-variables.md	Documents tidb_stmt_summary_group_by_user and tidb_stmt_summary_persist_evicted, including TiDB Cloud support restrictions, defaults, aggregation behavior, eviction persistence, and query effects.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Other

Suggested reviewers: qiancai

Merge Risk: ⚪ Minimal · up to ddd64

This change adds documentation for statement-summary variables and is ready to merge.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains the documentation changes, lists the affected variables and files, identifies the source PR, and records validation checks. It does not include the required TiDB version selec…	Add the required TiDB version section and select the applicable version, most likely v8.5. Include the relevant template headings where applicable.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the addition of statement summary system variables and includes the related PR number.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description explains the documentation changes, lists the affected variables and files, identifies the source PR, and records validation checks. It does not include the required TiDB version selection section, although the change targets the release-8.5 branch.

• Fix all pre-merge checks with AI

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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Actionable comments posted: 1

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ℹ️ Review info

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Configuration used: Path: .coderabbit.yaml

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Run ID: 73e03aeb-e5de-4e00-9a6e-1cf91692b5dc

📥 Commits

Reviewing files that changed from the base of the PR and between 6acba5d and 06a8e1a.

📒 Files selected for processing (3)

• statement-summary-tables.md
• system-variable-reference.md
• system-variables.md

Included review availability: Your plan provides up to 4 included reviews per hour; 3 remain after this review.