DBMS Basics - Interview Questions and Answers
What is cold backup and hot backup (in case of Oracle)?
- Cold Backup: It is copying the three sets of files (database files, redo logs, and control file) when
the instance is shut down. This is a straight file copy, usually from the disk directly to
tape. You must shut down the instance to guarantee a consistent copy.
If a cold backup is performed, the only option available in the event of data file loss
is restoring all the files from the latest backup. All work performed on the database
since the last backup is lost.
- Hot Backup: Some sites (such as worldwide airline reservations systems) cannot shut down the database while making a backup copy of the files. The cold backup is not an available option.
What is meant by Proactive, Retroactive and Simultaneous Update.
- Proactive Update: The updates that are applied to database before it becomes effective in real world.
- Retroactive Update: The updates that are applied to database after it becomes effective in real world.
- Simulatneous Update: The updates that are applied to database at the same time when it becomes effective in real world.