ClickHouse/docs/en/operations/settings/constraints_on_settings.md
2019-06-11 02:33:09 +03:00

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# Constraints on Settings
The constraints on settings can be defined in the `users` section of the `user.xml` configuration file and prohibit users from changing some of the settings with the `SET` query.
The constraints are defined as following:
```
<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>
```
If user tries to violate the constraints an exception is thrown and the setting isn't actually changed.
There are supported three types of constraints: `min`, `max`, `readonly`. The `min` and `max` constraints specify upper and lower boundaries for a numeric setting and can be used in combination. The `readonly` constraint specify that the user cannot change the corresponding setting at all.
**Example:** Let `users.xml` includes lines:
```
<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>
```
The following queries all throw exceptions:
```
SET max_memory_usage=20000000001;
SET max_memory_usage=4999999999;
SET force_index_by_date=1;
```
```
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.
```
**Note:** the `default` profile has a special handling: all the constraints defined for the `default` profile become the default constraints, so they restrict all the users until they're overriden explicitly for these users.
[Original article](https://clickhouse.yandex/docs/en/operations/settings/constraints_on_settings/) <!--hide-->