Add docs for Analyze Embedded in DDL and new system variable

[AilinKid]

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 (in Chinese).

• 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

[Copilot]

Pull Request Overview

This PR introduces documentation for the DDL Embedded Analyze optimization feature in TiDB v8.5.4. The feature allows DDL operations involving index creation or reorganization to automatically trigger inline statistics analysis.

Key Changes:

• Adds a new system variable tidb_stats_update_during_ddl to control DDL embedded analyze behavior
• Creates comprehensive documentation explaining DDL Embedded Analyze optimization for ADD INDEX and column modification operations
• Includes practical SQL examples demonstrating the feature for both new index creation and existing index reorganization scenarios

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
system-variables.md	Adds documentation for the new tidb_stats_update_during_ddl system variable introduced in v8.5.4
ddl_embedded_analyze.md	New documentation file explaining DDL Embedded Analyze optimization with detailed examples for index creation and column modification operations

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[ti-chi-bot]

@hawkingrei: adding LGTM is restricted to approvers and reviewers in OWNERS files.

In response to this:

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[AilinKid]

@hfxsd can this be merged before Fri? one of the big customer wait for this document in v8.5.4

[qiancai]

Rest LGTM

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-10-31 06:56:35.821661885 +0000 UTC m=+1632501.898914465: ☑️ agreed by tangenta.
• 2025-11-05 06:53:53.861156869 +0000 UTC m=+253083.304186738: ☑️ agreed by qiancai.

[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

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #21060.