Update for DM related docs

[dveeden]

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)

• Weaken the stance that we don't support foreign keys
• Mention binlog transaction compression in a few more places

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:
• 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, 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 refines the Data Migration (DM) documentation by updating details on foreign key compatibility and integrating explicit requirements for MySQL's binlog_transaction_compression setting. These changes aim to enhance the accuracy and completeness of the documentation, guiding users more effectively through the DM configuration process.

Highlights

• Foreign Key Documentation Clarification: The documentation's stance on foreign key support in TiDB DM has been softened from 'not supported' to 'not fully supported', providing a more accurate description of compatibility.
• Binlog Transaction Compression Requirement: Explicit requirements for binlog_transaction_compression=OFF have been added to the DM documentation, including precheck items and configuration examples, to ensure compatibility during data migration.

🧠 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.

Changelog

• dm/dm-compatibility-catalog.md
  • Updated table formatting for data sources.
• dm/dm-precheck.md
  • Clarified foreign key support from "not supported" to "not fully supported" in precheck descriptions.
  • Added a precheck item for binlog_transaction_compression=OFF.
  • Adjusted table formatting for precheck items.
• tidb-cloud/migrate-from-mysql-using-data-migration.md
  • Updated table formatting for data sources.
  • Added binlog_transaction_compression = OFF as a required binary log configuration.
  • Included binlog_transaction_compression in the SHOW VARIABLES command example.
  • Added binlog_transaction_compression = OFF to the example MySQL configuration.

Activity

• No additional activity (comments, reviews, or progress updates) has been recorded on this pull request since its creation.

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. ↩

[gemini-code-assist]

Code Review

This pull request updates documentation related to TiDB Data Migration (DM), primarily to clarify foreign key support and add information about binlog transaction compression. The changes correctly reflect that foreign keys are 'not fully supported' rather than 'not supported', and consistently add the binlog_transaction_compression=OFF requirement across relevant documents. The changes are well-aligned with the stated goals. I have one minor suggestion for stylistic consistency.

_{Note: Security Review has been skipped due to the limited scope of the PR.}

[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

[alastori]

Thanks for the binlog transaction compression additions — those are solid and well-placed across precheck + Cloud migration guide.

Two suggestions on the FK wording and a consistency nit. Context: TiDB fully supports foreign keys (GA since v8.5.0). The limitation is DM's replication behavior, not TiDB's FK support. There's an open issue tiflow#12129 specifically about the misleading DM warning message, and active engineering work on DM FK support this week (tiflow#12552, tiflow#12541, tiflow#12414). The compatibility catalog already correctly frames this as a DM limitation, not a TiDB limitation.

[alastori]

TiDB fully supports foreign keys (GA since v8.5.0). The issue is that DM doesn't replicate CASCADE operations correctly — it sets foreign_key_checks=OFF during replication. Saying "not fully supported by TiDB" misattributes the limitation. This aligns with the existing Incompatibility with foreign key CASCADE operations section in the compatibility catalog.

See also: tiflow#12129 (update misleading warning message).

Suggested change

	- Check whether the upstream tables have foreign keys, which are not fully supported by TiDB. A warning is returned if a foreign key is found in the precheck.
	- Check whether the upstream tables have foreign keys. DM does not replicate foreign key CASCADE operations (see [Incompatibility with foreign key CASCADE operations](/dm/dm-compatibility-catalog.md#incompatibility-with-foreign-key-cascade-operations)). A warning is returned if a foreign key is found in the precheck.