docs: support logging session connect attrs to slow query log

[jiong-nba]

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What is changed, added or deleted? (Required)

This PR updates docs according to pingcap/tidb#66617:

• Add Session_connect_attrs (json) to the schema examples of INFORMATION_SCHEMA.SLOW_QUERY and INFORMATION_SCHEMA.CLUSTER_SLOW_QUERY.
• Add the system variable doc for performance_schema_session_connect_attrs_size (default/range/-1 behavior/truncation/1 MiB hard limit note).
• Add status variable docs:
  • Performance_schema_session_connect_attrs_longest_seen
  • Performance_schema_session_connect_attrs_lost
• Update SESSION_CONNECT_ATTRS doc with size limit and truncation behavior.

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What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s):*: support logging session connect attrs to slow query log tidb#66617

Do your changes match any of the following descriptions?

• Delete files
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• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[pingcap-cla-assistant]

All committers have signed the CLA.

[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 synchronizes the documentation with recent changes in TiDB related to session connection attributes. It ensures that users have up-to-date information regarding the Session_connect_attrs column in slow query logs, the configuration options for connection attribute size limits, and new status variables for monitoring attribute usage and truncation.

Highlights

• Schema Updates: The Session_connect_attrs column (json type) has been added to the schema examples for INFORMATION_SCHEMA.SLOW_QUERY and INFORMATION_SCHEMA.CLUSTER_SLOW_QUERY.
• System Variable Documentation: Detailed documentation for the performance_schema_session_connect_attrs_size system variable has been added, covering its default value, range, behavior when set to -1, truncation logic, and a 1 MiB hard limit note.
• Status Variable Documentation: New status variables, Performance_schema_session_connect_attrs_longest_seen and Performance_schema_session_connect_attrs_lost, have been documented.
• SESSION_CONNECT_ATTRS Update: The SESSION_CONNECT_ATTRS documentation has been updated to include information about size limits and truncation behavior for connection attributes.

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Changelog

• information-schema/information-schema-slow-query.md
  • Added Session_connect_attrs column to the INFORMATION_SCHEMA.SLOW_QUERY schema example.
  • Updated row count in the INFORMATION_SCHEMA.SLOW_QUERY schema example.
  • Added Session_connect_attrs column to the INFORMATION_SCHEMA.CLUSTER_SLOW_QUERY schema example.
  • Updated row count in the INFORMATION_SCHEMA.CLUSTER_SLOW_QUERY schema example.
• performance-schema/performance-schema-session-connect-attrs.md
  • Added a new section titled 'Size limit and truncation' to the SESSION_CONNECT_ATTRS documentation.
  • Detailed the performance_schema_session_connect_attrs_size system variable's default, range, and -1 behavior.
  • Explained the truncation mechanism for excess attributes and the 1 MiB hard limit for handshake packets.
• status-variables.md
  • Added documentation for the Performance_schema_session_connect_attrs_longest_seen status variable.
  • Added documentation for the Performance_schema_session_connect_attrs_lost status variable.
• system-variable-reference.md
  • Inserted a new reference entry for performance_schema_session_connect_attrs_size.
• system-variables.md
  • Added a new section detailing the performance_schema_session_connect_attrs_size system variable.
  • Provided information on its scope, persistence, hint applicability, type, default value, range, unit, and behavior.
  • Included a note about the 1 MiB hard limit for handshake connection attributes.

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[gemini-code-assist]

Code Review

This pull request updates documentation to introduce and describe new features related to session connection attributes. It adds the Session_connect_attrs column to the information_schema.SLOW_QUERY table, documents the performance_schema_session_connect_attrs_size system variable for controlling attribute size limits and truncation, and introduces two new status variables (Performance_schema_session_connect_attrs_longest_seen and Performance_schema_session_connect_attrs_lost) for monitoring these attributes.

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

[Copilot]

Pull request overview

Updates TiDB documentation to reflect newly supported session connection attributes exposure and sizing/truncation behavior, syncing with upstream TiDB changes from pingcap/tidb#66617.

Changes:

• Document the new global system variable performance_schema_session_connect_attrs_size, including -1 behavior, truncation semantics, and the 1 MiB handshake hard limit.
• Add new status variables for monitoring observed/lost session connection attributes sizes.
• Extend schema examples and SESSION_CONNECT_ATTRS documentation to include Session_connect_attrs and size/truncation details.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
system-variables.md	Adds documentation for performance_schema_session_connect_attrs_size (defaults/range/truncation and hard limit note).
system-variable-reference.md	Adds cross-references for the new system variable entry.
status-variables.md	Documents new status variables tracking longest seen and truncated/lost session connect attrs.
performance-schema/performance-schema-session-connect-attrs.md	Adds a dedicated “Size limit and truncation” section tied to the new system variable and hard limit.
information-schema/information-schema-slow-query.md	Updates SLOW_QUERY and CLUSTER_SLOW_QUERY schema examples to include Session_connect_attrs and updates row counts.

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[jiong-nba]

/retest

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[jiong-nba]

/retest

[yibin87]

LGTM

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[lilin90]

/lgtm

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-03-30 07:46:47.132235817 +0000 UTC m=+164812.337595874: ☑️ agreed by lilin90.
• 2026-03-30 07:55:29.951846807 +0000 UTC m=+165335.157206864: ☑️ agreed by hfxsd.

[hfxsd]

/retest

[hfxsd]

/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hfxsd

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #22775.
But this PR has conflicts, please resolve them!