update description of max_execution_time for SELECT FOR UPDATE (#22055)

[ti-chi-bot]

This is an automated cherry-pick of #22055

What is changed, added or deleted? (Required)

Update the description of max_execution_time for SELECT FOR UPDATE statements.

Which TiDB version(s) do your changes apply to? (Required)

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• 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)?

pingcap/tidb#62960

• This PR is translated from: update description of max_execution_time for SELECT FOR UPDATE docs-cn#20944
• 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 focuses on enhancing the accuracy and clarity of the TiDB documentation regarding the max_execution_time system variable. The primary goal is to correct and refine the description of this variable's applicability, ensuring that users are fully aware that it governs the timeout for all SELECT statements, including those that involve locking rows with FOR UPDATE. This update helps prevent potential misunderstandings about SQL execution timeouts in various application contexts.

Highlights

• Documentation Clarification: The documentation for the max_execution_time system variable has been updated across several files to explicitly state that it applies to SELECT statements, including those with FOR UPDATE clauses. This clarifies its scope beyond just 'read-only SQL statements'.
• Scope of max_execution_time: The change provides a more precise definition of which SQL statements are affected by max_execution_time, ensuring users understand that SELECT ... FOR UPDATE operations are also subject to this timeout.

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[gemini-code-assist]

Code Review

This pull request updates the documentation to clarify that max_execution_time also applies to SELECT FOR UPDATE statements. The changes are consistent across most files. I've suggested a small addition to system-variables.md to ensure complete consistency with the other updated documents and the original intent of the change.

[qiancai]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

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