A view does not contain any data of its own, but is like a window through which data from other tables can be viewed and changed.
Information about the database, redologfile and datafile, archivelog file location and current scn no and redo log file
1. Database name and identifier.
2. Time stamp of database creation.
3. Tablespace names.
4. Backup information.
5. Checkpoint information.
6. Current online redo log file sequence number
Two processes wating to update the rows of a table which are locked by the other process then deadlock arises. In a database environment this will often happen because of not issuing proper row lock commands. Poor design of front-end application may cause this situation and the performance of server will reduce drastically.
These locks will be released automatically when a commit/rollback operation performed or any one of this processes being killed externally.
Deadlock is a kind of situation,which occured in a network of database environment while multiple processes is waiting for their completion, whereas some other process is still running till the time we use the rollback or commit commands or stopped the blocked process by database systems program itself.
The use of RollBack Segment is Database is - to maintain read consistency between multiple transactions.
Rollback segments are the areas in your database which are used to temporarily save the previous values when some updates (by 'updates', inserts or deletes as well) or any other transactions going on.