SQL> show parameter cluster_database;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
cluster_database                     boolean     TRUE

cluster_database_instances           integer     2

未实施RAC

SQL> show parameter cluster_database;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
cluster_database                     boolean     FALSE
cluster_database_instances           integer     1

CLUSTER_DATABASE is a Real Application Clusters parameter that specifies whether or not Real Application Clusters is enabled.

CLUSTER_DATABASE_INSTANCES is a Real Application Clusters parameter that specifies the number of instances that are configured as part of your cluster database. You must set this parameter for every instance. Normally you should set this parameter to the number of instances in your Real Application Clusters environment. A proper setting for this parameter can improve memory use.

Oracle uses the value of this parameter to compute the default value of the LARGE_POOL_SIZE parameter when the PARALLEL_AUTOMATIC_TUNING parameter is set to true. Note that the PARALLEL_AUTOMATIC_TUNIG parameter has been deprecated.

select * from v$option WHERE Parameter = \'Real Application Clusters\';

Output:True/False

V$OPTION displays Oracle Database options and features. Typically, although not always, options must be separately licensed, whereas features come with the product and are enabled based on the product that is running (Standard Edition, Enterprise Edition, and so on).

方法3：

SELECT * from v$active_instances;

INST_NUMBER        INST_NAME
1                       xyzdb1:abprod1
2                       xyzdb2:abprod2

V$ACTIVE_INSTANCES displays the mapping between instance names and instance numbers for all instances that have the database currently mounted.