Release 2 (8.1.6)
Part Number A76961-01
This chapter describes the dynamic performance views, which are often referred to as V$ views.
Oracle contains a set of underlying views that are maintained by the 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.
Although these views appear to be regular database tables, they are not. These views provide data on internal disk structures and memory structures. You can select from these views, but you can never update or alter them.
CATALOG.SQL script contains definitions of the views and public synonyms for the dynamic performance views. You must run
CATALOG.SQL to create these views and synonyms. After installation, only username SYS or anyone with
SYSDBA role has access to the dynamic performance tables.
The actual dynamic performance views are identified by the prefix V_$. Public synonyms for these views have the prefix V$. Database administrators and other users should access only the V$ objects, not the V_$ objects.
The dynamic performance views are used by Enterprise Manager and Oracle Trace, which is the primary interface for accessing information about system performance. Once the instance is started, the V$ views that read from memory are accessible. Views that read data from disk require that the database be mounted, and some require that the database be open.
For almost every V$ view described in this chapter, Oracle has a corresponding GV$ (global V$) view. In a parallel server environment, querying a GV$ 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
INST_ID column displays the instance number from which the associated V$ view information was obtained. The INST_ID column can be used as a filter to retrieve V$ information from a subset of available instances. For example, the query:
retrieves the information from the V$ views on instances 2 and 5.
In order to query the GV$ views, the value of the
PARALLEL_MAX_SERVERS parameter must be greater than zero on all instances mounting the database.
The sections that follow list the columns and public synonyms for the dynamic performance views.
Press the "Next" button to go to the first dynamic performance view.