# Scope of TiDB System Parameters

__*TiDB system configuration scope*__
__*TiDB system variable scope*__

![left](./student-guide/diagram/SystemParametersScope_aa_001_20220617.png)
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TiDB system parameters have their own scopes. Variables can be global scope (global scope), instance scope (instance scope), session scope (session scope), or a combination of the above scopes. Among them:

- Changes to the GLOBAL scope variable will only take effect for new TiDB connection sessions after setting it, and the current active connection session will not be affected. The changes will be persistent and will remain in effect after a restart.

- Changes to the INSTANCE scope variable will take effect immediately for all active or new connection sessions of the current TiDB instance after setting it. Other TiDB instances will not take effect. Changes will not be persisted, and will not be valid after restart TiDB.

GLOBAL scoped variables are persisted through kv storage and are not persisted to the TiDB configuration file, so don't worry that operation and administer such as tiup upgrade and tiup reload will overwrite the configuration file and will not cause the modify to fail, because the persistence of this modify does not depend on the configuration file.

The scope is session level or instance level. Variables can only be temporarily modified and will not be persisted. Therefore, if you want to persist, you need to manually modify the configuration file of the target TIDB-Server and use tiup edit-config to edit the parameters, but you don't need to execute tiup reload (this operation will restart indiscriminately).