Create unique DB_NAME and DB_DOMAIN for an Oracle 11g instance

instanceoracleoracle-11g-r2

I am somewhat confused by these terms in the init.ora file:

  1. db_domain
  2. db_name
  3. instance_name

plus the database name which is provided to the create database command. I do not completely understand how they sum up. I have read the Oracle docs several times but still failed to understand.
As far as I understand, a database can be mounted and used by several instances in a RAC which I do not use. This means that db_name has to be the same as in create database?!

This is my setup:

I have 2 machines host1, host2. Both are in the same subdomain dom1.company.net. Both have an instance which hosts the same database but one in for the production system and the other one is the test system.

If I name both data, do I have a name collision?

Thanks for clearing up.

Best Answer

No, you do not have a name collision. Your DB_DOMAIN, DB_NAME, and INSTANCE_NAME can all be identical as long as the databases are on different hosts (as you have indicated). However, as others have stated using the same DB_NAME is a bad idea for anything other than perhaps a recovery operation. A policy enforcing distinct passwords will be broken. Connections will be confused. Most things you can do to ensure that changes are not inadvertently made on production are probably worth the hassle.

Here is the relevant documentation:

DB_DOMAIN

In a distributed database system, DB_DOMAIN specifies the logical location of the database within the network structure. You should set this parameter if this database is or ever will be part of a distributed system. The value consists of the extension components of a global database name, consisting of valid identifiers (any alphanumeric ASCII characters), separated by periods.

Note: Oracle recommends that you specify DB_DOMAIN as a unique string for all databases in a domain.

This parameter allows one department to create a database without worrying that it might have the same name as a database created by another department. If one sales department's DB_DOMAIN is JAPAN.ACME.COM, then their SALES database (SALES.JAPAN.ACME.COM) is uniquely distinguished from another database with DB_NAME = SALES but with DB_DOMAIN = US.ACME.COM.

If you omit the domains from the name of a database link, Oracle expands the name by qualifying the database with the domain of your local database as it currently exists in the data dictionary, and then stores the link name in the data dictionary.

DB_NAME

DB_NAME specifies a database identifier of up to 8 characters. This parameter must be specified and must correspond to the name specified in the CREATE DATABASE statement.

If you have multiple databases, the value of this parameter should match the Oracle instance identifier of each one to avoid confusion with other databases running on the system. The value of DB_NAME should be the same in both the standby and production initialization parameter files.

INSTANCE_NAME

In a Real Application Clusters environment, multiple instances can be associated with a single database service. Clients can override Oracle's connection load balancing by specifying a particular instance by which to connect to the database. INSTANCE_NAME specifies the unique name of this instance.

In a single-instance database system, the instance name is usually the same as the database name.

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