sys-var: clarify tidb_slow_log_rules syntax/behavior and de-duplicate slow log docs

[hfxsd]

What is changed, added or deleted? (Required)

This PR refactors and clarifies tidb_slow_log_rules documentation in:

• system-variables.md
• identify-slow-queries.md

Main updates:

1. Reorganized tidb_slow_log_rules in system-variables.md with clearer structure:

   • Unified syntax and constraints
   • Type constraints
   • Full field table (type/unit/summary)
   • Effective behavior and matching order
   • Examples and usage recommendations

2. Clarified key behavior/constraints:

   • SESSION/GLOBAL rule capacity and separators
   • SESSION does not support Conn_ID (GLOBAL only)
   • Matching semantics (>= for numeric, = for string/bool)
   • Rule update behavior (SET overwrites, not appends)
   • Fallback to tidb_slow_log_threshold when no effective rules
   • String values cannot contain , / ; (quoted values still not supported)
   • Repeated fields in one rule: last value wins
   • Time-unit distinction (tidb_slow_log_rules time fields are seconds, threshold is milliseconds)

3. Reduced duplication between docs:

   • Kept rule contract/details in system-variables.md
   • Added metric interpretation section in identify-slow-queries.md
   • Replaced repeated long explanations with cross-references

Which TiDB version(s) do your changes apply to? (Required)

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• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)

What is the related PR or file link(s)?

• This PR is translated from: sys-var: clarify tidb_slow_log_rules syntax/behavior and de-duplicate slow log docs docs-cn#21337

• Fix issue: 完善 tidb_slow_log_rules 文档：字段/单位/取值范围（min-max）与语法约束 docs-cn#21324
• Other reference link(s): executor, variable: support cop_mvcc_read_amplification to trigger printing slow log tidb#66064

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[gemini-code-assist]

Summary of Changes

Hello, 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 significantly enhances the clarity and accuracy of the documentation for the tidb_slow_log_rules system variable. By reorganizing content, clarifying specific behaviors and constraints, and reducing redundancy across related documents, it aims to provide users with a more comprehensive and easier-to-understand guide for configuring and interpreting slow log rules, ultimately improving their ability to identify and troubleshoot performance issues.

Highlights

• Documentation Refactoring: The documentation for tidb_slow_log_rules has been refactored and clarified across system-variables.md and identify-slow-queries.md to improve user understanding.
• system-variables.md Enhancements: system-variables.md now features a reorganized structure for tidb_slow_log_rules, including unified syntax, type constraints, a full field table, effective behavior, matching order, and usage examples.
• Behavior Clarifications: Key behaviors and constraints of tidb_slow_log_rules have been clarified, covering SESSION/GLOBAL rule capacity, Conn_ID support, matching semantics, rule update behavior, fallback mechanisms, string value limitations, handling of repeated fields, and time-unit distinctions.
• Duplication Reduction: Duplication between documentation files has been reduced by centralizing rule contract details in system-variables.md and adding metric interpretation to identify-slow-queries.md, utilizing cross-references for efficiency.

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Changelog

• temp.md
  • Added a test file for demonstration purposes.

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[gemini-code-assist]

Code Review

The pull request description indicates significant documentation updates for tidb_slow_log_rules. However, the provided changes only consist of adding a temp.md file, which seems unrelated to the stated purpose and appears to be a temporary file. This file should be removed from the pull request to ensure the changes accurately reflect the PR's goal. My review includes a minor suggestion for this file in case its inclusion is intentional.

I am having trouble creating individual review comments. Click here to see my feedback.

temp.md (1)

It is a best practice for text files to end with a newline character. This ensures file integrity and proper processing by various tools like cat and git.

This is a test file.

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-03-18 10:02:37.458067472 +0000 UTC m=+351284.545724999: ☑️ agreed by zimulala.