Why service_names in init.ora?

Dear all,

We know that db_name, db_domain, instance_name and service_names are the most basic settings in init.ora. Obviously, instance_name is SID, unique on a machine, so host + SID (+ protocol) makes a tnsnames.ora (or connect string) entry; db_name + db_domain (= global database name) is unique on the network, so host + db_name.db_domain (or service_name in tnsnames.ora term) also makes a tnsnames.ora entry. However, I still don't know why service_names exists in addition to db_name and db_domain. Look at the doc:

<<quote Oracle8i Reference begin>>

SERVICE_NAMES
Parameter type: String  

Syntax: SERVICE_NAMES =

db_service_name [, db_service_name [,...] ]  

Parameter class: Static  

Default value: DB_NAME.DB_DOMAIN if defined  

Range of values: Any ASCII string or comma-separated list of string names  

SERVICE_NAMES specifies one or more names for the database service to which this instance connects. You can specify multiple services names in order to distinguish among different uses of the same database. For example:

SERVICE_NAMES = sales.acme.com, widgetsales.acme.com   

You can also use service names to identify a single service that is available from two different databases through the use of replication.

In an Oracle Parallel Server environment, you must set this parameter for every instance.

If you do not qualify the names in this parameter with a domain, Oracle qualifies them with the value of the DB_DOMAIN parameter. If DB_DOMAIN is not specified, Oracle uses the domain of your local database as it currently exists in the data dictionary.  

See Also:

Net8 Administrator's Guide for more information on this parameter and its settings.

"DB_DOMAIN".
<<quote Oracle8i Reference end>>

service_names is pretty much the same thing as db_name + db_domain except that service_names is plural, which means one instance or one database has one or more service_names? What are the 'different uses of the same database'? Anyone knows this? Thanks in advance.

Dino Received on Mon Sep 03 2001 - 21:08:35 CDT