Do not merge until v8.5.4: doc updates for v8.5.4

[qiancai]

What is changed, added or deleted? (Required)

This PR covers all doc updates for v8.5.4 that have been merge to the feature/preview-v8.5.4 branch.

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: Do not merge until v8.5.4: doc updates for v8.5.4 docs-cn#21061
• 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 @qiancai, 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 consolidates a comprehensive set of documentation updates for the upcoming TiDB v8.5.4 release. The changes introduce new SQL statements for fine-grained control over table Region distribution, enhance DDL operations by embedding automatic statistics collection for indexes, and improve compatibility with MySQL's DECIMAL behavior. Furthermore, the documentation for the Follower Read feature has been significantly refined, global indexes now support non-unique columns, and the new TiCDC architecture's monitoring is better integrated. These updates aim to provide users with clear, up-to-date information on new features and behavioral changes in the latest TiDB version.

Highlights

• New DDL Statements for Region Distribution: Introduced DISTRIBUTE TABLE, CANCEL DISTRIBUTION JOB, SHOW DISTRIBUTION JOBS, and SHOW TABLE DISTRIBUTION statements to manage and monitor table Region distribution across TiFlash and TiKV nodes.
• Embedded ANALYZE in DDL Statements: Added a new feature that automatically runs ANALYZE (statistics collection) during ADD INDEX, MODIFY COLUMN, and CHANGE COLUMN operations, ensuring prompt statistics updates for new or reorganized indexes and preventing suboptimal query plans. This is controlled by the new tidb_stats_update_during_ddl system variable.
• MySQL Compatibility for DECIMAL: TiDB v8.5.4 now aligns its DECIMAL data type behavior with MySQL, automatically truncating extra decimal places during insertion, regardless of their count.
• Enhanced Follower Read Documentation: Updated the Follower Read documentation with clearer usage scenarios, detailed replica selection strategies (leader, closest-replicas, closest-adaptive), performance overhead considerations, and new monitoring metrics in Grafana.
• Global Indexes for Non-Unique Columns: Global indexes for partitioned tables now support non-unique indexes, expanding their utility beyond unique keys.
• TiCDC New Architecture Monitoring Integration: The TiCDC-New-Arch monitoring dashboard is now integrated into Grafana for TiDB clusters v8.5.4 and later, simplifying monitoring setup.
• New TiFlash Configuration: Added graceful_wait_shutdown_timeout for TiFlash, allowing configuration of the maximum wait time for unfinished MPP tasks during server shutdown.
• New Optimizer System Variables: Introduced tidb_opt_enable_no_decorrelate_in_select and tidb_opt_enable_semi_join_rewrite system variables to control optimizer behavior for subqueries.

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[gemini-code-assist]

Code Review

This pull request includes documentation updates for TiDB v8.5.4. The changes cover new features like ANALYZE embedded in DDL, DISTRIBUTE TABLE, and new system variables. The documentation for Follower Read, partitioned tables, and TiCDC has also been significantly improved for clarity and accuracy.

Overall, the updates are well-written and provide valuable information for users. I have one minor suggestion for grafana-tidb-dashboard.md to ensure consistency in metric descriptions. The rest of the changes are excellent.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-11-19 07:25:28.773385311 +0000 UTC m=+82892.422579768: ☑️ agreed by hfxsd.

[ti-chi-bot]

@hfxsd: Your lgtm message is repeated, so it is ignored.

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