1. Session - 17 RECOVERY CONTROL - 2 Matakuliah: M0184 / Pengolahan Data Distribusi Tahun: 2005 Versi:

2. OBJECTIVE Cause of failure that need recovery Basic Recovery Step

3. CAUSE OF FAILURE Transaction-local failure Site failure Media failure Network failure

4. Transaction-local failure Transaction-induced abort, for example the “No Fund” example. The application programmer has written code to trap particular error Unforeseen Transaction failure arising from bugs in application (example : arithmetic error such as division by zero) System-induced abort which occurs when transaction manager explicitly aborts a transaction because it conflict with another transaction

5. SITE FAILURES As a result of the Local CPU or a power supply failure, all transaction on that machine are affected In DDB environment since site operate independently from each other, it is possible for some sites to be operational while others have failed If all sites down, this is called total failure, if only some have failed, the it refer to partial failure

6. SITE FAILURES Cont’d In order to recover from site failure, local recovery manager first of all has to find out the state of the local system at the time of failure Restore the DB to a consistent state by undoing or redoing transaction according to their status at the time of failure.

7. MEDIA FAILURE DB being corrupted, the common cause is a disk head crash The objective of recovery manager is to restore the last committed values of all data object Two possible approach : archiving or mirroring

8. MEDIA FAILURE Cont’d Archiving can be done by taking backup from DB archive. It is desirable that the backup copy is made when the system is quiescent, otherwise the backup may contain partial update which complicate its use for recovery Mirroring is allows two complete copies of the DB to be maintained on-line on different stable storage device

9. NETWORK FAILURE DDBMS depend on the ability of all sites in the network to be able to communicate reliably with one another In the event of line failure, many network support automatic re-routing of message

10. Basic Recovery Step