About Dynamic Performance Views

Oracle contains a set of underlying views that are maintained by the database server and accessible to the database administrator user SYS. These views are called dynamic performance views because they are continuously updated while a database is open and in use, and their contents relate primarily to performance.

1)V$ Views:
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Though many of us may already know that those name which prefixed by V$ are original dynamic performance view but they are not really views; they are public synonyms of the view. The actual dynamic performance views are identified by the prefix V_$. Database administrators and other users should access only the V$ objects, not the V_$ objects.


2)GV$ Views
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For almost every V$ view, Oracle has a corresponding GV$ (global V$) view. In Real Application Clusters, querying a GV$ view retrieves the V$ view information from all qualified instances. In addition to the V$ information, each GV$ view contains an extra column named INST_ID of datatype NUMBER. The INST_ID column displays the instance number from which the associated V$ view information was obtained. For example, the following query retrieves the information from the V$LOCK view on instances 3 and 5:

SQL> SELECT * FROM GV$LOCK WHERE INST_ID = 3 OR INST_ID = 5;