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69 lines
2.3 KiB
Markdown
69 lines
2.3 KiB
Markdown
# Constraints on Settings
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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.
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The constraints are defined as following:
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```
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<profiles>
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<user_name>
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<constraints>
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<setting_name_1>
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<min>lower_boundary</min>
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</setting_name_1>
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<setting_name_2>
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<max>upper_boundary</max>
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</setting_name_2>
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<setting_name_3>
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<min>lower_boundary</min>
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<max>upper_boundary</max>
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</setting_name_3>
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<setting_name_4>
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<readonly/>
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</setting_name_4>
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</constraints>
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</user_name>
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</profiles>
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```
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If user tries to violate the constraints an exception is thrown and the setting isn't actually changed.
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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.
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**Example:** Let `users.xml` includes lines:
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```
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<profiles>
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<default>
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<max_memory_usage>10000000000</max_memory_usage>
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<force_index_by_date>0</force_index_by_date>
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...
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<constraints>
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<max_memory_usage>
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<min>5000000000</min>
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<max>20000000000</max>
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</max_memory_usage>
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<force_index_by_date>
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<readonly/>
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</force_index_by_date>
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</constraints>
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</default>
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</profiles>
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```
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The following queries all throw exceptions:
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```
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SET max_memory_usage=20000000001;
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SET max_memory_usage=4999999999;
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SET force_index_by_date=1;
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```
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```
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Code: 452, e.displayText() = DB::Exception: Setting max_memory_usage should not be greater than 20000000000.
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Code: 452, e.displayText() = DB::Exception: Setting max_memory_usage should not be less than 5000000000.
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Code: 452, e.displayText() = DB::Exception: Setting force_index_by_date should not be changed.
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```
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**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.
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[Original article](https://clickhouse.yandex/docs/en/operations/settings/constraints_on_settings/) <!--hide-->
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