Matakuliah
Tahun
Versi
: M0184 / Pengolahan Data Distribusi
: 2005
:
Session - 17
RECOVERY CONTROL - 2
OBJECTIVE
• Cause of failure that need recovery
• Basic Recovery Step
CAUSE OF FAILURE
•
•
•
•
Transaction-local failure
Site failure
Media failure
Network failure
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
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
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.
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
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
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
Basic Recovery Step