Update follower read and learner read descriptions (#21470)

[ti-chi-bot]

This is an automated cherry-pick of #21470

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)

The description of follower-read and learner-read is inaccurate, and related behaviors have been adjusted in the newer version of tidb, so the corresponding documentation has been revised accordingly.

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: Update follower read and learner read descriptions docs-cn#20609
• Other reference link(s):

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 updates the documentation for TiDB's follower-read and learner-read functionalities. The changes clarify the system's behavior regarding replica selection, including the consideration of learner replicas for follower reads and the fallback mechanisms to leader/follower replicas when the primary target (follower or learner) is unavailable. It also provides important version-specific details for older TiDB releases.

Highlights

• Follower Read Behavior Update: The documentation for tidb_replica_read set to follower has been updated to reflect that learner replicas are now considered for reads with the same priority, and if no follower or learner replicas are available, TiDB will read from the leader replica.
• Learner Read Behavior Update: The description for tidb_replica_read set to learner has been revised to state that if no learner replica is available, TiDB will read from an available leader or follower replica.
• Version-Specific Clarification: A new note has been added to clarify the behavior for TiDB v7.5.0 and earlier versions, where setting tidb_replica_read to follower or learner would result in an error if no corresponding replicas were available.

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

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. ↩

[gemini-code-assist]

Code Review

This pull request does a good job of updating the descriptions for follower-read and learner-read to reflect their current behavior. The changes to use the active voice and address the user directly with 'you' are a great improvement and align well with the documentation style guide.

However, this change has been applied inconsistently. While some list items were updated, others describing tidb_replica_read values still use the older, passive phrasing. For a more consistent user experience, I recommend updating all items in this list to use the active voice in a follow-up PR.

I've also left one specific suggestion to improve the clarity of a note by simplifying its sentence structure.

[hfxsd]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hfxsd

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

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [hfxsd]

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