I've searched this topic in Google and there are several information, but it makes me confused more..
At first, I thought SID is the unique key for "database" not "instance", and must be matched with "DB_NAME".
However, In a post, it says SID doesn't need to match DB NAME, global name, unique name, and instance name.. with some practical configuration. In another post, it says SID is combination of database name + instance number..
In my short knowledge,
Instance is server ORACLE processes are running, which contains SGA.
Database is just storage that user applications' data is stored. When instance runs, it access to DB, mount the control files, open the data files and redo logs.
If the above comment is right, I think SID must be Database, and.. could be DB_NAME..
Now I'm confusing Database, Instance, SID, and DB_NAME.
Thank you for reading..