tidb: update the default value of tidb_analyze_column_options (#22198) #22309
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Summary of ChangesHello @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 updates the default behavior of the Highlights
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Code Review
This pull request updates the default value of tidb_analyze_column_options to ALL and adjusts the documentation accordingly. The changes are generally good, but I have a couple of suggestions to improve the clarity and completeness of the documentation for better user understanding.
| - Default value: `PREDICATE` | ||
| - Default value: `ALL` | ||
| - Value options:`ALL`, `PREDICATE` | ||
| - This variable controls the behavior of the `ANALYZE TABLE` statement. Setting it to `PREDICATE` means only collecting statistics for [predicate columns](/statistics.md#collect-statistics-on-some-columns); setting it to `ALL` means collecting statistics for all columns. In scenarios where OLAP queries are used, it is recommended to set it to `ALL`, otherwise collecting statistics can result in a significant drop in query performance. |
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For better clarity, I suggest rephrasing the last part of this sentence. The current wording 'otherwise collecting statistics can result in a significant drop in query performance' is a bit confusing. It could be interpreted as 'collecting statistics is bad if not set to ALL'. A clearer phrasing would explain why the performance drops.
| - This variable controls the behavior of the `ANALYZE TABLE` statement. Setting it to `PREDICATE` means only collecting statistics for [predicate columns](/statistics.md#collect-statistics-on-some-columns); setting it to `ALL` means collecting statistics for all columns. In scenarios where OLAP queries are used, it is recommended to set it to `ALL`, otherwise collecting statistics can result in a significant drop in query performance. | |
| - This variable controls the behavior of the `ANALYZE TABLE` statement. Setting it to `PREDICATE` means only collecting statistics for [predicate columns](/statistics.md#collect-statistics-on-some-columns); setting it to `ALL` means collecting statistics for all columns. In scenarios where OLAP queries are used, it is recommended to set it to `ALL` to avoid a significant drop in query performance that might result from incomplete statistics. |
References
- The suggested change improves the clarity and readability of the documentation, making it easier for users to understand the impact of the variable setting. This aligns with the style guide's emphasis on clarity and simplicity. (link)
| | [`tidb_enable_non_prepared_plan_cache`](/system-variables.md#tidb_enable_non_prepared_plan_cache)| Enable the [Non-prepared plan cache](/sql-non-prepared-plan-cache.md) feature to reduce compile costs for applications that do not use prepared statements. | N/A | | ||
| | [`tidb_ignore_prepared_cache_close_stmt`](/system-variables.md#tidb_ignore_prepared_cache_close_stmt-new-in-v600)| Cache plans for applications that use prepared statements but close the plan after each execution. | N/A | | ||
| | [`tidb_analyze_column_options`](/system-variables.md#tidb_analyze_column_options-new-in-v830)| Collect statistics for all columns to avoid suboptimal execution plans due to missing column statistics. By default, TiDB only collects statistics for [predicate columns](/statistics.md#collect-statistics-on-some-columns). | Setting this variable to `'ALL'` can cause more resource usage for the `ANALYZE TABLE` operation compared with the default value `'PREDICATE'`. | | ||
| | [`tidb_analyze_column_options`](/system-variables.md#tidb_analyze_column_options-new-in-v830)| Collect statistics for all columns to avoid suboptimal execution plans due to missing column statistics. | N/A | |
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The note for tidb_analyze_column_options has been changed to N/A. While the previous note was outdated due to the change in the default value, providing no note at all reduces the completeness of the documentation. A brief note explaining the trade-off of using the non-default PREDICATE value would be helpful for users.
| | [`tidb_analyze_column_options`](/system-variables.md#tidb_analyze_column_options-new-in-v830)| Collect statistics for all columns to avoid suboptimal execution plans due to missing column statistics. | N/A | | |
| | [`tidb_analyze_column_options`](/system-variables.md#tidb_analyze_column_options-new-in-v830)| Collect statistics for all columns to avoid suboptimal execution plans due to missing column statistics. | Setting this variable to `PREDICATE` can reduce resource usage for the `ANALYZE TABLE` operation, but might lead to suboptimal execution plans. | |
References
- The documentation should be complete. Replacing a useful note with 'N/A' reduces completeness. The suggestion provides a concise and helpful note about the trade-offs of the available options. (link)
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This is an automated cherry-pick of #22198
First-time contributors' checklist
What is changed, added or deleted? (Required)
ref pingcap/tidb#64994
Updated the default value of
tidb_analyze_column_optionstoALL.Which TiDB version(s) do your changes apply to? (Required)
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