system-variables: add optimizer cost factors (#20748) #21602
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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 updates the documentation for TiDB system variables, specifically adding and refining descriptions for various optimizer cost factors. This ensures that the documentation accurately reflects the internal cost model variables used by the TiDB optimizer.
Highlights
- Documentation Refinement: Minor wording adjustments were made to existing tidb_opt_*_factor system variables, clarifying their internal use within the cost model.
- New Optimizer Cost Factors: Documentation for 16 new system variables related to optimizer cost factors has been added. These variables, such as tidb_opt_hash_agg_cost_factor and tidb_opt_index_join_cost_factor, are introduced for TiDB versions v8.5.3 and v9.0.0.
- Internal Use Warning: All newly documented cost factor variables include a warning that they are for internal use by the cost model and are not recommended for manual modification.
- Standardized Properties: The new variables are consistently defined with Float type, a range of [0, 2147483647], a default value of 1, and are applicable to SESSION | GLOBAL scope, supporting the SET_VAR hint.
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Code Review
This pull request adds documentation for a set of new optimizer cost factor system variables. The changes are well-structured. I have a couple of suggestions to improve consistency and completeness, which I've added as comments on the first new variable tidb_opt_hash_agg_cost_factor. These suggestions apply to all the new variables added in this PR.
- Variable names in headings should be wrapped in backticks for consistency with the rest of the document and to adhere to the style guide.
- Each new variable should have a brief description of what it does to make the documentation more complete and helpful for users.
| - Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes | ||
| - Type: Float | ||
| - Range: `[0, 2147483647]` | ||
| - Default value: `1` |
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To improve clarity and completeness, please add a brief description of what this variable controls. This comment applies to all the new tidb_opt_*_cost_factor variables added in this pull request.1
For example, for tidb_opt_hash_agg_cost_factor, you could add the following bullet point to its property list:
- This variable is used to adjust the cost of the HashAgg operator.Style Guide References
Footnotes
| - Default value: `OFF` | ||
| - This variable is used to control whether to allow `INSERT`, `REPLACE`, and `UPDATE` statements to operate on the `_tidb_rowid` column. This variable can be used only when you import data using TiDB tools. | ||
| ### tidb_opt_hash_agg_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span> |
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For consistency with other variable headings in this document and to adhere to the style guide, please wrap the system variable name in backticks.1
This suggestion applies to all new tidb_opt_*_cost_factor variables added in this pull request.
| ### tidb_opt_hash_agg_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span> | |
| ### `tidb_opt_hash_agg_cost_factor` <span class="version-mark">New in v8.5.3 and v9.0.0</span> |
Style Guide References
Footnotes
…auto-embed * commit 'b570cc86270ba2e2b2b71d6eab8d717c2c8a1c56': (48 commits) *: remove TiDB roadmap from TOC, home, index, add warning (#21628) (#21637) Update the scope of system-variable ”tidb_redact_log“ (#21513) (#21634) *: add custom Japanese localization for cloud docs (#21612) Modify the introduction of `cop_pool_size` (#21462) (#21627) tiflash: Update tiflash upgrade guide (#21619) (#21625) Update tidb-performance-tuning-config.md (#21621) (#21624) Update tidb-cloud-poc.md (#21336) (#21411) cloud: update the pricing link for starter (#21620) ticdc: clarify descriptions of `index-value` and `columns` (#21616) (#21617) release-8.5: remove 'v' prefix from tidb-version variable (#21614) release-8.5: update version to 8.5.3 (#21613) cloud: fix note annotation syntax for proper rendering (#21611) ticdc: add key word for redo log (#21564) (#21607) ticdc: correct the tiup cluster command (#21135) (#21608) bump TiDB from v8.5.2 to v8.5.3 (#21578) v8.5.3: add release notes (#21399) (#21606) v8.5.3: log backup: update metafile format (#21412) (#21577) v8.5.3: update telemetry related doc files (#21404) (#21603) system-variables: add optimizer cost factors (#20748) (#21602) Add more description about SHARD_ROW_ID_BITS (#21467) (#21600) ...
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This is an automated cherry-pick of #20748
First-time contributors' checklist
What is changed, added or deleted? (Required)
Documented all of the new optimizer cost factors.
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.
What is the related PR or file link(s)?
Do your changes match any of the following descriptions?