The Oracle system identifier (SID) identifies a specific instance of the running Oracle software. For a Real Application Clusters database, each node within the cluster has an instance referencing the database. The database name, specified by the DB_NAME parameter in the INITDB_NAME.ORA file, and unique thread ID make up each node's SID. The thread ID starts at 1 for the first instance in the cluster, and is incremented by 1 for the next instance, and so on.
A unique name for an Oracle instance. To switch between Oracle databases, users must specify the desired SID. The SID is included in the CONNECT DATA parts of the connect descriptor in a tnsnames.ora file, and in the definition of the network listener in a listener.ora file.
A unique name for a database instance. To switch between databases, users must specify the desired SID. The SID is included in the CONNECT DATA parts of the connect descriptors in a TNSNAMES.ORA file, and in the definition of the network listener in the LISTENER.ORA file. If you choose the default configuration, the SID defaults to "*".