Useful Dynamic Performance (V$) Views

V$ Views vs GV$ Views:V$ views are CONTAINER_DATA objects. When a user connected to the root queries a V$ view, the query results will depend on the CONTAINER_DATA attribute for users. For almost every V$ view,  Oracle has a corresponding GV$ (global V$) view. In Oracle Real Application Clusters, querying a GV$ 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 data type NUMBER. The INST_ID column displays the instance number from which the associated V$ view information was obtained.
V$ACCESS displays objects in the database that are currently locked and the sessions that are accessing them.V$ACTIVE_INSTANCES displays the mapping between instance names and instance numbers for all instances that have the database currently mounted.V$AQ displays statistics for the queues in the database.V$CONTEXT lists set attributes in the current session.V$CONTROLFILE lists the names of the control files.V$DATABASE displays information about the database from the control file.V$DATAFILE contains datafile information from the control file.V$DBFILE lists all datafiles making up the database. This view is retained for historical compatibility. Use of V$DATAFILE is recommended instead.V$DBLINK describes all database links (links with IN_TRANSACTION = YES) opened by the session issuing the query on V$DBLINK. These database links must be committed or rolled back before being closed.V$INSTANCE view displays the state of the current instance.V$LICENSE contains information about license limits.V$NLS_PARAMETERS view contains current values of NLS parameters. =>NLS_CALENDAR, NLS_CHARACTERSET, NLS_CURRENCY, NLS_DATE_FORMAT, NLS_DATE_LANGUAGE, NLS_ISO_CURRENCY, NLS_LANGUAGE, NLS_NUMERIC_CHARACTERS, NLS_SORT, NLS_TERRITORY, NLS_UNION_CURRENCY, NLS_NCHAR_CHARACTERSET, NLS_COMPV$NLS_VALID_VALUES lists all valid values for NLS parameters. V$OBJECT_USAGE to monitor index usage. The view displays statistics about index usage gathered from the database. All indexes that have been used at least once can be monitored and displayed in this view. V$OPTION lists options that are installed with the Oracle Database.V$PARAMETER displays information about the initialization parameters that are currently in effect for the session. A new session inherits parameter values from the instance-wide values displayed by the V$SYSTEM_PARAMETER view.V$PARAMETER2 displays information about the initialization parameters that are currently in effect for the session, with each list parameter value appearing as a row in the view. A new session inherits parameter values from the instance-wide values displayed in the V$SYSTEM_PARAMETER2 view.Presenting the list parameter values in this format enables you to quickly determine the values for a list parameter. For example, if a parameter value is a, b, then the V$PARAMETER view does not tell you if the parameter has two values (both a and b) or one value (a, b). V$PARAMETER2 makes the distinction between the list parameter values clear.V$SESSION view lists session information for each current session.V$SGA displays summary information about the system global area (SGA).V$SQL lists statistics on shared SQL area without the GROUP BY clause and contains one row for each child of the original SQL text entered.V$SQL_BIND_DATA For each distinct bind variable in each cursor owned by the session querying this view/V$SQL_PLAN contains the execution plan information for each child cursor loaded in the library cache.V$SQL_PLAN_STATISTICS provides execution statistics at the row source level for each child cursor.V$SQLTEXT contains the text of SQL statements belonging to shared SQL cursors in the SGA.V$VERSION displays version numbers of core library components in the Oracle Database.