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optimizer-fix-control: add doc for the new optimizer fix controls introduced in v7.3.0 #14535

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Aug 7, 2023
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optimizer-fix-control: add doc for the new optimizer fix controls introduced in v7.3.0 #14535

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time-and-fate Jul 17, 2023
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time-and-fate Jul 18, 2023
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add description for non-prepared plan cache
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ran-huang Jul 27, 2023
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21 changes: 21 additions & 0 deletions optimizer-fix-controls.md
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Expand Up @@ -37,3 +37,24 @@ SET SESSION tidb_opt_fix_control = '44262:ON,44389:ON';
- 默认值：`OFF`
- 可选值：`ON`、`OFF`
- 对形如 `c = 10 and (a = 'xx' or (a = 'kk' and b = 1))` 的过滤条件，是否尝试为 `IndexRangeScan` 更加完整地构造扫描范围，即 `range`。

### [`44823`](https://github.com/pingcap/tidb/issues/44823) <span class="version-mark">从 v7.3.0 版本开始引入</span>

- 默认值：`200`
- 可选值：`[0, 2147483647]`
- 为了节省内存，对于参数超过 `200` 个的查询，Plan Cache 将不会缓存。
- 这个开关用来调节这个参数，`0` 表示无限制。
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### [`44830`](https://github.com/pingcap/tidb/issues/44830) <span class="version-mark">从 v7.3.0 版本开始引入</span>

- 默认值：`OFF`
- 可选值：`ON`、`OFF`
- 此开关控制是否让 Plan Cache 对在物理优化阶段形成的 `PointGet` 计划进行缓存。

### [`44855`](https://github.com/pingcap/tidb/issues/44855) <span class="version-mark">从 v7.3.0 版本开始引入</span>

- 默认值：`OFF`
- 可选值：`ON`、`OFF`
- 在某些场景下，当 `IndexJoin` 算子的 `Probe` 端包含 `Selection` 算子时，TiDB 会严重高估 `IndexScan` 的行数，导致在 `IndexJoin` 更好的时候选择了其它的执行计划。
- TiDB 已经引入了缓解这类问题的逻辑。但是由于潜在的计划回退风险，该逻辑并没有被默认启用。
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- 此开关控制是否让这个改进生效。
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