Some important V$ views

I cannot stop myself to share a few great views which provide excellent information

V$SGA :
We can get information about the system global area (SGA)

V$SGA_DYNAMIC_COMPONENTS:
Can get information about the dynamic SGA components. This summy provides details based on all completed SGA resize operations since instance startup. All sizes are expressed in bytes.

V$SGAINFO:

Can get information about the SGA, including the sizes of different SGA components, the granule size, and free memory.

V$SGASTAT

We can get detailed information on the system global area (SGA).

V$SHARED_SERVER

We can get information on the shared server processes.

V$TABLESPACE

Can get tablespace information from the control file

V$TRANSACTION

Can get lists the active transactions in the system.

V$TRANSACTION_ENQUEUE
displays locks owned by transaction state objects.

V$VERSION

We can get version numbers of core library components in the Oracle Database.


V$LOGFILE

This view contains information about redo log files.

V$BACKUP_DATAFILE_DETAILS:
We can get information about restorable datafiles. It will include all datafiles backed in the backup set, image copies, and proxy copies.

Please browse the Oracle link to explore more views
http://docs.oracle.com/cd/B19306_01/server.102/b14237/toc.htm