# TiDB Configuration Types

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![`smart`](./student-guide/diagram/TiDBConfiguration_aa_001_20220617.png)
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`TiDB` system variables belong to `TiDB` server, they are not related to `Placement Driver (PD)` and `TiKV` servers. Many server variables are dynamic and can be set at runtime using `SET GLOBAL` or `SET SESSION`. These values can also be obtained using `SELECT`. `TiDB` system variables are persisted in the database storage.

The cluster configuration covers the configurations of `TiDB` server, `TiKV` server, and `Placement Driver (PD)` server. Those configurations are stored on the corresponding server nodes as configuration files, and they can be modified by using `TiUP` utility.


System variables:
- Some system variables are stored in the `TiKV` KV storage.
- Some system variables are stored in the `TiDB` server configuration file.
- They are scoped.
- Can be modified via `MySQL Client`.
- Modifications to some variables do not require a restart to persist.
- Valid for `TiDB` servers only.

Cluster parameters:
- All parameters are stored in the configuration files of `TiDB` servers, `TiKV` servers, and `PD` servers.
- They are not scoped.
- Modify and take effect by `tiup edit-config` and `tiup reload`.