What is the role of SID in Oracle?

In Oracle database, SID (System Identifier) refers to the unique identifier of a database instance. Each Oracle database instance has a unique SID used to distinguish different instances in the database.

The roles of SID include:

1. The unique identifier, SID, is used to uniquely identify a database instance, ensuring that different database instances running on the same physical server can be distinguished from each other.
2. Connecting to the database: When a user wants to connect to an Oracle database instance, the correct SID must be provided. By specifying the correct SID, users can connect to the desired database instance.
3. Manage database instances: Switch or control between multiple database instances by using the SID. Administrators can use the SID to stop, start, restart, or manage database instances.
4. Monitoring and management: The SID can be used to identify the running database instance for monitoring and management purposes. It can be used to view the status, performance metrics, and log information of the database instance.
5. Configure and manage database resources: In Oracle database, you can use SID to configure and manage database resources, such as setting and allocating memory, disk space, connection numbers, etc.

In conclusion, SID is an important parameter used in Oracle databases to uniquely identify and connect database instances, as well as to control, manage, and configure database resources.