Oracle db_name vs oracle_unique_name (RAC , data guard and MAA

 

Names Among MAA

Under Oracle Maximum Availability Architecture (MAA), we might be confused about various kinds of name. Here I try to clarify these names by chart and table.

DB_NAME (Enterprise-wide Name)

You must set this parameter for every instance in order to startup the database. If you didn't assign DB_NAME at installation-time, then

DB_NAME = $ORACLE_SID

DB_UNIQUE_NAME (Site-wide Name)

If you didn't assign DB_UNIQUE_NAME in the parameter file at startup-time, then

DB_UNIQUE_NAME = DB_NAME

If you didn't assign SERVICE_NAMES in the parameter file at startup-time, then

SERVICE_NAMES = DB_UNIQUE_NAME

INSTANCE_NAME (Server-wide Name)

If you didn't assign INSTANCE_NAME in the parameter file at startup-time, then

INSTANCE_NAME = $ORACLE_SID

Naming Scope and Default Values

Parameter Name	Name Scope	Default Value	Level
DB_NAME	Enterprise-wide	= $ORACLE_SID (Installation-time)	Database
DB_UNIQUE_NAME	Site-wide	= DB_NAME (Startup-time)	Role
SERVICE_NAMES	Site-wide (or Enterprise-wide)	= DB_UNIQUE_NAME (Startup-time)	Role (or Database)
INSTANCE_NAME	Server-wide	= $ORACLE_SID (Startup-time)	Instance
$ORACLE_SID	Server-wide	N/A	Instance

The above featured image illustrates you a hierarchy tree for better understanding on the relationship among names. For more details, you may check DB_NAME and DB_UNIQUE_NAME in Oracle documentation.