ClickHouse/docs/zh/operations/settings/constraints-on-settings.md

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---
# 对设置的限制 {#constraints-on-settings}
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在设置的约束可以在定义 `profiles` 一节 `user.xml` 配置文件,并禁止用户更改一些设置与 `SET` 查询。
约束定义如下:
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``` xml
<profiles>
<user_name>
<constraints>
<setting_name_1>
<min>lower_boundary</min>
</setting_name_1>
<setting_name_2>
<max>upper_boundary</max>
</setting_name_2>
<setting_name_3>
<min>lower_boundary</min>
<max>upper_boundary</max>
</setting_name_3>
<setting_name_4>
<readonly/>
</setting_name_4>
</constraints>
</user_name>
</profiles>
```
如果用户试图违反约束,将引发异常,并且设置不会更改。
支持三种类型的约束: `min`, `max`, `readonly`. 该 `min``max` 约束指定数值设置的上边界和下边界,并且可以组合使用。 该 `readonly` constraint指定用户根本无法更改相应的设置。
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**示例:** 让 `users.xml` 包括行:
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``` xml
<profiles>
<default>
<max_memory_usage>10000000000</max_memory_usage>
<force_index_by_date>0</force_index_by_date>
...
<constraints>
<max_memory_usage>
<min>5000000000</min>
<max>20000000000</max>
</max_memory_usage>
<force_index_by_date>
<readonly/>
</force_index_by_date>
</constraints>
</default>
</profiles>
```
以下查询都会引发异常:
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``` sql
SET max_memory_usage=20000000001;
SET max_memory_usage=4999999999;
SET force_index_by_date=1;
```
``` text
Code: 452, e.displayText() = DB::Exception: Setting max_memory_usage should not be greater than 20000000000.
Code: 452, e.displayText() = DB::Exception: Setting max_memory_usage should not be less than 5000000000.
Code: 452, e.displayText() = DB::Exception: Setting force_index_by_date should not be changed.
```
**注:** 该 `default` 配置文件具有特殊的处理:所有定义的约束 `default` 配置文件成为默认约束,因此它们限制所有用户,直到为这些用户显式复盖它们。
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[原始文章](https://clickhouse.tech/docs/en/operations/settings/constraints_on_settings/) <!--hide-->