Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

planner: change default of tidb_opt_prefer_range_scan #18609

Merged
merged 2 commits into from
Oct 15, 2024
Merged

planner: change default of tidb_opt_prefer_range_scan #18609

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
260744a
Update system-variables.md
hfxsd Sep 11, 2024
4470563
Update system-variables.md
hfxsd Sep 11, 2024
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
8 changes: 6 additions & 2 deletions system-variables.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -3871,12 +3871,16 @@ mysql> desc select count(distinct a) from test.t;

### `tidb_opt_prefer_range_scan` <span class="version-mark">从 v5.0 版本开始引入</span>

> **注意：**
>
> 从 v8.4.0 开始，此变量的默认值从 `OFF` 更改为 `ON`。

- 作用域：SESSION | GLOBAL
- 是否持久化到集群：是
- 是否受 Hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value) 控制：是
- 类型：布尔型
- 默认值：`OFF`
- 将该变量值设为 `ON` 后，优化器总是偏好区间扫描而不是全表扫描。
- 默认值：`ON`
- 该变量值为 `ON` 时，对于没有统计信息的表（伪统计信息）或空表（零统计信息），优化器将优先选择区间扫描而不是全表扫描。
- 在以下示例中，`tidb_opt_prefer_range_scan` 开启前，TiDB 优化器需要执行全表扫描。`tidb_opt_prefer_range_scan` 开启后，优化器选择了索引区间扫描。

```sql
Expand Down