When an update process is executed,
“pre-update” and “post-update”
information is saved to the log file
Database
Log file
(journal file)
Pre-update information
Post-update information
Backup
Ba
Database
② Back up database
from specific point in time
(save it)
3
ck
up
Log file
① Back up log file when
it becomes full (save it)
Recovery process
The “recovery process” is the process of restoring the database to the
state it was in when it was backed up or just before the trouble arose in the
event of hardware or software failure.
There are two types of recovery processes, “roll forward” and “roll
back.”
●Roll forward
“Roll forward” describes the method of restoring a database to the state it
was in when the log file was backed up by using the database backup, and
reproducing the processes listed in the log file in the event of hardware
failure or other issues.
●Roll back
“Roll back” describes the method of rewinding the data back to before the
transaction, and starting again in the event an error occurs during a transaction.
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