Update system-variables.md

[qiancai]

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• master (the latest development version)
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What is the related PR or file link(s)?

• This PR is translated from: Update system-variables.md docs-cn#15
• Other reference link(s):

Do your changes match any of the following descriptions?

• Delete files
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• Need modification after applied to another branch
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Summary by CodeRabbit

• Documentation
  • Added documentation for a new system variable that controls the optimizer’s default selectivity when statistics are insufficient (introduced in v9.0.0).
  • Describes scopes (SESSION and GLOBAL), cluster persistence, and control via query hint.
  • Specifies valid range [0, 1] with a default of 0.8.
  • Includes guidance noting it’s generally not recommended to modify this value.

[gemini-code-assist]

Summary of Changes

Hello @qiancai, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request, titled "Update system-variables.md", appears to be an attempt to introduce documentation for new system variables related to optimizer selectivity and executor concurrency in TiDB, as suggested by the PR description and an automated summary. However, the only change reflected in the provided patch is the addition of a temporary markdown file named "temp.md" containing a simple test string. This suggests a potential mismatch between the stated intent and the actual file changes presented for review.

Highlights

• Temporary File Addition: A new file named "temp.md" has been added to the repository, containing the text "This is a test file.".
• Intended Documentation Updates (Not in Patch): The pull request description and an automated summary indicate an intention to update "system-variables.md" to document new "tidb_opt_selectivity_factor" and per-operator executor concurrency controls. However, these specific documentation changes are not present in the provided patch.

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[gemini-code-assist]

Code Review

This pull request adds a new file temp.md. However, the title and description indicate that the goal was to update system-variables.md. The added file seems unrelated to the stated purpose of the PR and might have been included by mistake. My review is based on the file change provided.

[github-actions]

🤖 Auto-sync completed successfully

📥 Source PR: qiancai/docs-cn#15
🎯 Target PR: #49
✅ English documentation has been updated based on Chinese documentation changes.

This comment was generated automatically by the sync workflow.

[coderabbitai]

Walkthrough

Documentation update adds a new system variable entry for tidb_opt_selectivity_factor to system-variables.md, detailing scope, persistence, type, range, default, control via SET_VAR hint, purpose, and a note discouraging modification.

Changes

Cohort / File(s)	Summary
Docs: System Variables system-variables.md	Added documentation for new variable tidb_opt_selectivity_factor (v9.0.0): SESSION/GLOBAL scope, persisted to cluster, controllable via query hint SET_VAR; float [0,1], default 0.8; used when statistics cannot derive predicate selectivity; note advising against modification.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

I twitch my whiskers, read the lore,
A factor new—selectivity’s core!
From zero to one, set just right,
It guides the planner through the night.
I hop, I nod: docs aligned—
0.8 by default, optimization in mind.

Pre-merge checks and finishing touches

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Description Check	⚠️ Warning	The PR description includes the contribution template but leaves all required sections blank, including the summary of changes and the affected version checklist, and the CLA checkbox is not marked, making it incomplete.	Please complete the PR description by filling in the “What is changed, added or deleted?” section with a clear summary, selecting the affected TiDB version(s), and checking the CLA confirmation.
Title Check	❓ Inconclusive	The title “Update system-variables.md” is too generic and does not convey the primary change of the pull request, which is adding the new tidb_opt_selectivity_factor system variable.	Please revise the title to clearly summarize the main change, for example “Add tidb_opt_selectivity_factor system variable to system-variables.md.”

✅ Passed checks (1 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changes. Docstring coverage check skipped.

✨ Finishing touches

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch test-add-a-variable-15

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

system-variables.md (1)

1794-1803: Match field labels to existing style for consistency.

All other variable entries use the “Persists to cluster”, “Applies to hint [SET_VAR]”, “Type”, and “Range” labels. This new block switches to “Is persisted to the cluster”, “Is controlled by the Hint”, “Type: Floating-point number”, and “Value range”. Please align the labels and wording with the existing convention to keep the reference uniform—for example:

• Persists to cluster: Yes
• Applies to hint …: Yes
• Type: Float
• Range: [0, 1]

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 322c671 and d07ddad.

📒 Files selected for processing (1)

• system-variables.md (1 hunks)

🧰 Additional context used

📓 Path-based instructions (1)

**/*.md

⚙️ CodeRabbit configuration file

As a technical writer in the database area, you need to first learn the changes in this PR, and then improve the content to make it clear, concise, and easy to understand in English according to your database knowledge.

Files:

• system-variables.md