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planner: add new cascades planner document #20470

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AilinKid Jun 5, 2025
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lilin90 Aug 19, 2025
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Avoid pre-announce feature
lilin90 Aug 19, 2025
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4 changes: 2 additions & 2 deletions system-variables.md
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Expand Up @@ -1754,9 +1754,9 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;

### `tidb_enable_cascades_planner`

> **警告：**
> **注意：**
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@lilin90 lilin90 Sep 15, 2025 •
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Since "Cascades Planner" is listed in TiDB 功能概览 | TiDB 文档中心, please confirm whether we need to update the status in that table. Till v8.5, the feature status is experimental. Is it GA in v9.0?

>
> 目前 cascades planner 为实验特性，不建议在生产环境中使用。
> 目前 cascades planner 为全新的优化器框架实现，其在设计之初就是为了兼容性出发考虑的，其可以在最大程度上保证和原有优化器逻辑的兼容性，并且在逻辑层面能够给到一定的扩展空间，此外还能够在多重逻辑计划之间进行 CBO 决策。目前 cascades planner 开启之后由于逻辑 rule 的数量目前还比较有限，其做 plan 的能力不一定会显现出很大的提升，但是随着后续 [TiDB Cascades Rule Evolution Project](https://github.com/pingcap/tidb/issues/61528) 项目的不断深入，cascades planner 将会展现更大的灵活性和适用性。
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@lilin90 lilin90 Sep 10, 2025 •
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> 目前 cascades planner 为全新的优化器框架实现，其在设计之初就是为了兼容性出发考虑的，其可以在最大程度上保证和原有优化器逻辑的兼容性，并且在逻辑层面能够给到一定的扩展空间，此外还能够在多重逻辑计划之间进行 CBO 决策。目前 cascades planner 开启之后由于逻辑 rule 的数量目前还比较有限，其做 plan 的能力不一定会显现出很大的提升，但是随着后续 [TiDB Cascades Rule Evolution Project](https://github.com/pingcap/tidb/issues/61528) 项目的不断深入，cascades planner 将会展现更大的灵活性和适用性。
> Cascades planner 是 TiDB 引入的一种全新的优化器框架。该框架充分考虑了与现有优化器逻辑的兼容性，并在逻辑层面预留了扩展空间。借助这一框架，优化器能够在多个候选逻辑执行计划之间进行基于代价的优化 (Cost-Based Optimization, CBO) 决策。
>
> 目前，当开启 cascades planner 时，由于逻辑规则 (rule) 数量有限，生成的执行计划在性能上未必有显著提升。但随着 [TiDB Cascades Rule Evolution Project](https://github.com/pingcap/tidb/issues/61528) 的推进，cascades planner 将逐步展现更大的灵活性和适用性，为复杂查询场景提供更好的优化能力。


- 作用域：SESSION | GLOBAL
- 是否持久化到集群：是
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