Using the above log files and backup files, DB2 UDB can support database
recovery by various methods and to
different levels:
Crash/restart recovery
This is a technique for an automated database recovery to recover the
database to a stage where all the transactions are completed and committed.
This is done by rolling back incomplete transactions and completing
committed transactions that were still in memory when the crash occurred.
This is done automatically by the database manager if you set the automatic
restart (autorestart) database configuration parameter to
ON
by:
db2>db2 update database configuration for itsodb2 using autorestart ON
or by restarting the database when a database failure occurs; this is done by
calling:
db2>restart database itsodb2
DB2 UDB maintains log files, the recovery history file, and table space
change history file to recover data that is lost or damaged.
Version recovery
This is recovery option used for non recoverable databases or databases
without achieved logs. In this recovery option, previous backup versions of
the database are restored in case of an emergency. Typically, database
backups are taken in tapes and kept in remote places.
It is very necessary to take a backup on regular basis because this recovery
method loses the changes made in database after backup. This is done by
restoring the database using incremental, delta, or full backup.
Rollforward recovery
In rollforward recovery, you can specify the local time to which you want to roll
forward your database. In this method backup data is used in conjugation with
database transaction records to achieve a goal of taking DB2 UDB to the
state immediately before the failure. Figure 8 2 shows the roll forward
recovery technique of DB2 UDB.
Chapter 8. Database administration
239
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