Journalizing facilities - which maintain an audit trail of transaction and database changes.
Check point facility - by which the DBMS periodically suspends all processing and synchronized its file and journals to establish a recovery point.
Recovery manager - Which allows the DBMS to restore the database to a correct condition and restart processing transaction.
Backup facilities
A DBMS produce a backup copy (or save) of an entire database or subset of a database.
This copy include following database objects, repository, database index, or source libraries.
Backup copy is produce at least one per day.
WHY? - The backup copy is used to restore the database in the event of hardware failure, catastrophic loss or damage.
Backup Methods
cold backup- Also called offline backup. cold backup mean, a database backup during which the database is offline and not accessible to update.
HOT backup- Only a selected portion of the database is shutdown from use. then do the backup process.
Incremental backup- Type of backup that only copies files that have changed since the previous backup.
Fall backup- The DBMS will automatically make backup copies of the database in real time.
Recovery Techniques
Disk mirroring- Two copies of the database must be kept update simultaneously. when media failure occurs switched to the duplicate copy of the database.
Restore/Return- A technique that involves re processing the day's transactions against the backup copy of the database.
Maintain transaction integrity- Follow the ACID properties.
Rollback(Backward) Recovery- The back out or undo , of unwanted changes to a database. rollback is used to reverse the changes made by transaction that have been aborted or terminated abnormally.
Roll forward recovery- A technique that start with an earlier copy of a database. the results of good transactions are applied to the database, and the database quickly moved forward to a later state.
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