Dynamic Views

V$SGA	The V$SGA view is useful in determining how much total memory is allocated to the various componentsof the SGA. The following simple query gives you a summary of the SGA memory usage bythe current instance:	SQL> SELECT * FROM V$SGA;
V$SGASTAT	The V$SGASTAT view gives you a detailed breakdown of the SGA memory. It shows you currentmemory allocations broken down into the following main areas:	SQL> SELECT bytes from v$sgastat2 WHERE pool='shared pool' and3 V$SGA name='free memory'
V$SESSION	The V$SESSION view gives you a wealth of information about the users, including their operatingsystem username, terminal name, whether they’re actively executing a transaction or just connectedto the database, and how long their connection has been in place. In Oracle Database 10g,the V$SESSION view also contains several wait-related columns such as WAIT_CLASS_ID, WAIT_CLASS#, WAIT_CLASS, WAIT_TIME, and SECONDS_IN_WAIT.
V$SESSION_LONGOPS	The V$SESSION_LONGOPS view shows the status of all operations that run for a long time (morethan six seconds in absolute time). The columns SOFAR and TIME_REMAINING indicate how much ofthe work is done and how long the operation has to go before completing. The following is a samplequery using the view:	SQL> SELECT sid, opname, sofar,totalwork,2 start_time, time_remaining3* FROM V$SESSION_LONGOPS;
V$LOGFILE	The V$LOGFILE view provides information about each redo log file, including its name andwhether the file is valid or not. The STATUS column has the following values:	SQL> SELECT * FROM V$LOGFILE;
V$ARCHIVED_LOG	The V$ARCHIVED_LOG view is essential when you’re looking at information regarding whicharchive logs you have access to. The view contains one entry for every log that your databasearchives. When you restore an archive log, the operation inserts one row	SQL> SELECT name, thread#, sequence#,2 archived, applied, deleted, completion_time3* FROM V$ARCHIVED_LOG;
V$ARCHIVE_DEST	As its name indicates, the V$ARCHIVE_DEST view shows you each archive log destination and itsstatus. This view has a large number of columns, and you need to pay special attention to the followingcolumns:	SQL> SELECT dest_name2 FROM V$ARCHIVE_DEST;
V$SYSSTAT	The V$SYSSTAT view provides you with all the major system statistics: parse statistics, executionrates, full table scans, and other performance indices. The V$SYSSTAT view provides you with thebuffer-cache hit ratios and a number of other hit ratios. Listing 23-31 shows a summary of the mainclasses of statistics contained in the V$SYSSTAT view.	SQL> SELECT * FROM V$SYSSTAT;
V$OSSTAT	The new V$OSSTAT view comes in handy when you wish to check system usage statistics.