For Oracle, we mount the instance to the database or mount the database to the instance

instanceoracle

The following text is extract from oracle documentation.

Start the instance, and mount and open
the database. This can be done in
unrestricted mode, allowing access to
all users, or in restricted mode,
allowing access for database
administrators only.

….

To mount a database to a previously
started, but not opened instance, use
the SQL statement ALTER DATABASE with
the MOUNT clause as follows:

ALTER DATABASE MOUNT;

You can read it directly from http://download.oracle.com/docs/cd/B19306_01/server.102/b14231/start.htm

The first part gives me an impression that we are mounting the instance to the database. But the To mount a database to a previously started, but not opened instance part gives me an impression that we are mounting database to an instance.

Which one understanding is right? Anyone can help to explain it please?

Thanks

Best Answer

We are mounting a database to an instance. See the concepts guide:

The instance mounts a database to associate the database with that instance.

One way I've seen it explained (probably here or on SO) is that the instance is the memory structures and processes, and the database is the data on disk. The instance has to have a database associated with it to be able to do anything useful.

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