Most properties are dynamic; that means you can set them while Derby is running, and their values change without requiring a reboot of Derby. In some cases, this change takes place immediately; in some cases, it takes place at the next connection.
Some properties are static, which means changes to their values will not take effect while Derby is running. You must restart or set them before (or while) starting Derby.
For more information, see Making dynamic or static changes to properties.