SPM: add binding usage

[hawkingrei]

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[gemini-code-assist]

Summary of Changes

Hello @hawkingrei, 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 enhances the SQL Plan Management documentation by introducing a dedicated section on 'Binding Usage'. This addition aims to provide users with comprehensive information on how to track and manage the usage of SQL bindings, thereby facilitating better optimization and maintenance of query performance through the identification and handling of unused bindings.

Highlights

• New Documentation Section: A new section titled 'Binding Usage' has been added to the sql-plan-management.md document.
• Binding Usage Explanation: The new section explains how 'Binding Usage' helps collect statistics for SQL bindings, aiding in the identification and management of unused bindings to optimize query performance.
• System Variable: The tidb_enable_binding_usage system variable is introduced, which controls the collection of usage statistics for SQL plan bindings.
• Usage Query Example: An example SQL query is provided to demonstrate how to retrieve binding usage statistics, specifically the sql_digest and last_used_date from the mysql.bind_info table.

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[gemini-code-assist]

Code Review

This pull request adds a new section on 'Binding Usage' to the SQL Plan Management documentation. The changes are good, but I've suggested a few improvements for clarity, conciseness, and consistency with the documentation style guide. Specifically, I've recommended using sentence case for the heading, rephrasing the descriptive paragraphs to be more direct and use active voice, and formatting the SQL example to use uppercase keywords for consistency.

[gemini-code-assist]

This suggestion improves clarity and conciseness. It also uses active voice as recommended by the style guide¹ and clarifies that the usage information is written to the mysql.bind_info table.

Suggested change

	Binding Usage helps you collect usage statistics of SQL bindings, which can assist you in identifying and managing unused bindings. You can use these statistics to optimize your binding management strategy, such as removing bindings that are no longer needed or adjusting existing bindings to improve query performance.
	You can use the `tidb_enable_binding_usage` system variable to control whether to enable the usage statistics collection for SQL plan bindings. When this variable is set to `ON`, every six hours, the usage of bindinfo will be written into TiKV.
	The binding usage feature helps you collect usage statistics for SQL bindings. You can use these statistics to identify and manage unused bindings, for example, by removing bindings that are no longer needed or adjusting existing ones to improve query performance.
	You can use the `tidb_enable_binding_usage` system variable to control the collection of usage statistics for SQL plan bindings. When this variable is set to `ON`, TiDB writes the binding usage information to the `mysql.bind_info` table every six hours.

Style Guide References

Footnotes

1. The style guide recommends avoiding overuse of passive voice. ↩

[gemini-code-assist]

For consistency with other examples in this document, SQL keywords should be in uppercase. Also, this removes an extra space after from.

Suggested change

	select sql_digest,last_used_date from mysql.bind_info limit 1;
	SELECT sql_digest, last_used_date FROM mysql.bind_info LIMIT 1;