Oracle Database - System Identifier (SID)

The System Identifier (SID) identifies a specific database instance. The SID uniquely distinguishes the instance from any other instance on the same computer. Each database instance requires a unique SID and database name. In most cases, the SID is the same as the database name portion of the global database name.

A name that identifies a specific instance of a running pre-release 8.1 Oracle database. For any database, there is at least one instance referencing the database.

For pre-release 8.1 databases, SID is used to identify the database. The SID is included in the connect descriptor of a tnsnames.ora file and in the definition of the listener in the listener.ora file.

Each instance have an unique name :

• When a database is created, a name is associated with it and stored in its control files.
• When an heterogeneous services source is created, an SID refer to it

If the destination service is:

• an Oracle8i or later release database, then use Service Name
• an Oracle release 8.0 database, then use the SID

To change the name of an existing database, you must use the CREATE CONTROLFILE statement to re-create your control files and specify a new database name.