recovery management

Recovery management with
concurrent controls
D. Shanmugapriya
II-Msc (IT)
Department of CS & IT
Nadar saraswathi college of arts and science
Theni.

Recovery Management
• Recovery manager is a utility that manages the
process of creating backups of all database files.
• Is the process of restoring the database to the most
recent consistent state that existed just failure the
system.
• Is the process of planning,testing and
implementing the recovery procedures and
standards required to restore service in the event
of a component failure.

3 states of recovery
• Pre-condition:In a consistant state.
• Condition:Occurs some kind of system failure.
• Post condition:Restore the data base to the
consistent state of the existed before the failure.

Types
• Transaction failure :Occurs when it fails to execute or when
it reaches a point from where it can’t go any further. If a
few transaction is hurt this is called as transaction
failure.(incorrect IP, deadlock)
• System failure :May result from a hard drive with bad
sectors, causing the operating system to not able to read
data from the hard drive. (is failure, ram failure).
• Media failure :A condition of not being able to read from
or write to a storage device such as a disk or tape due to a
defect in the recording surface. (power problem).

Database basic update strategies
• Deferred update:Transaction operating do not immediately
update the physical database.
• Database is physically updated only after the transaction
reaches it’s commit point.
• Immediate update:database is immediately updated by
the transaction operation during the execution of
transactions even before it reaches commit point.
• Example :word-to save the file and immediately updated.

Concurrent control
• The process of managing simultaneous operation on the
database without having them interface with each other.
• The problem of synchronizing concurrent transaction
such that the consistency of the database of the
maintained same time.
• Concurrent controls invlove identifying and preventing
problems in a organizing as they occur this means that as
they occur.

Why we need concurrency control
• Simultaneous execution of transaction over a shared
database can create several data integrity and consistency
problem.
• Three types
• 1)lost update
• 2)temporary uodate
• 3)incorrect summary

Lost update
• This problem occurs when two transactions that access
the same database items.
• Have their operation interlaced in a way that makes the
values of same database item incorrect.
• Successfully completed update is overridden by another
user.
• Example:T1 withdraws $10 from an account with
balance initially $ 100.
• T2 deposits $100 into same accoint
• Serially final balance would be $190.

Temporary update
• This problem occurs when one transaction updates a
database item and then the transaction fails for some
reasons.
• The updated item is accessed by another transactions
before it is changed back to its original value.
• Example :T4 updates balance to 200 but it aborts so
balance should be back at original value 100
• T3 has read new value of balance 200 and users value as
basis of 10 reduction giving a new balance of 190 instead
of 90.

Advantage
• Waiting time decrease
• Response time decrease.
• Resourse utilization increase.
• Efficiency utilization increase.

recovery management

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