Matakuliah
Tahun
Versi
: M0184 / Pengolahan Data Distribusi
: 2005
:
Session - 15
RECOVERY CONTROL - 1
OBJECTIVES
• What is backup and recovery
• Why we need recovery
• Recovery manager
Backup and Recovery
• Backup is a copy of data. This copy
includes important parts of your database
such as the control file and data files. A
backup is a safeguard against unexpected
data loss and application errors; should
you lose your original data, you can use
the backup to make it available again.
Backup and Recovery Cont’d
• Recovery in general refers to the
various operations involved in
restoring, rolling forward, and rolling
back a backup.
Backup and Recovery Cont’d
Backup and recovery in general
refers to the various strategies and
operations involved in protecting your
database against data loss and
reconstructing the data should that
loss occur.
Restoring and Recovering a Database
Why we need recovery ?
• The ability to ensure consistency of the DB
in presence of unpredictable failures of
both software and hardware components
is an essential feature of any DBMS.
• The role of recovery manager of the
DBMS to restore the DB to a consistent
state.
Recovery Manager
• Recovery manager has to ensure that, on
recovery from failure, either all the effects
of a given transaction are permanently
recorded in the DB or none of them
• The principal function of the recovery
manager following failure is to identify
which transaction have to be undone and
which have to be redone, and then
perform the necessary undo and redo
operations. the
Recovery Manager Cont’d
The DB Log (also called Journal or Audit trail
plays an essential role in this recovery.
Audit trail or journal that can be used for
anticipating failure are :
• Log File
• Checkpoint