br: add variable tidb_advancer_check_point_lag_limit to control log backup checkpoint lag (#21481)

[ti-chi-bot]

This is an automated cherry-pick of #21481

First-time contributors' checklist

• I've signed the Contributor License Agreement, which is required for the repository owners to accept my contribution.

What is changed, added or deleted? (Required)

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

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• 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: br: add variable tidb_advancer_check_point_lag_limit to control log backup checkpoint lag docs-cn#20710
• Other reference link(s): br: add global variable to control checkpoint lag limit tidb#62680

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 @ti-chi-bot, 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 integrates a new system variable, tidb_advancer_check_point_lag_limit, into TiDB's documentation. This variable provides a crucial mechanism for managing log backup tasks by automatically pausing them if their checkpoint lag surpasses a configurable threshold. This enhancement aims to improve the stability and reliability of log backup operations by preventing tasks from falling excessively behind.

Highlights

• New System Variable: Introduced tidb_advancer_check_point_lag_limit to control the maximum checkpoint lag for log backup tasks.
• Log Backup Control: This variable allows TiDB Advancer to pause log backup tasks if their checkpoint lag exceeds the defined limit, preventing potential issues.
• Documentation Update: Added comprehensive documentation for the new system variable, detailing its scope, type, default value, range, and purpose.

🧠 New Feature in Public Preview: You can now enable Memory to help Gemini Code Assist learn from your team's feedback. This makes future code reviews more consistent and personalized to your project's style. Click here to enable Memory in your admin console.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please ask for approval from hfxsd. For more information see the Code Review Process.
Please ensure that each of them provides their approval before proceeding.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[gemini-code-assist]

Code Review

This pull request adds documentation for the new system variable tidb_advancer_check_point_lag_limit. The change is well-structured and clear. I have one minor suggestion to improve clarity by using a more general term instead of an internal component name, making it easier for users to understand.

[gemini-code-assist]

For better clarity and consistency with other variable descriptions, consider replacing the internal component name 'TiDB Advancer' with 'TiDB'. This makes the documentation easier for users to understand, as 'TiDB Advancer' is not defined elsewhere.

Suggested change

	- This variable controls the maximum allowed checkpoint lag for a log backup task. If a task's checkpoint lag exceeds this limit, TiDB Advancer pauses the task.
	- This variable controls the maximum allowed checkpoint lag for a log backup task. If a task's checkpoint lag exceeds this limit, TiDB pauses the task.

References

1. The style guide emphasizes clarity and making documentation easy to understand for users (Lines 14, 21). The term 'TiDB Advancer' is not defined elsewhere and could be confusing. Using 'TiDB' is clearer and more consistent with other descriptions. ^(link)