Dbms Group Presentation

8/6/2019 Dbms Group Presentation

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Presented by, Naga mahesh

Nupur Roy

Md Mojahid Islam

Mukesh Narayn

Nithin Joseph



DATA BASE RECOVERY SYSTEMDATA BASE RECOVERY SYSTEM�The recovery system is an integral part of the database

system.

�System crash due to hardware failure r software errors

r logical errors in the program that is accessing the

database.

�The no. of recovery techniques depends on the

atomicity property of transactions.



Transaction: A single unit of work in which all

operations must b applied and completed to

produce a consistent database.

The database recovery process generally

follows a predictable scenario.

It first determines the type and extent of the

required recovery.



y If the entire database need to be recovered to aconsistent state the recovery uses the most recentbackup copy of the database is known as consistentstate.

y The backup copy is then rolled forward to restore allsubsequent transactions by using the transaction loginformation.

y If the database needs to be recovered but the committedportion of the database is still unstable , the recoveryprocess uses the transaction log to undo all thetransactions that were not committed.



y Some DBMS s provide functions that

allows the DBA to schedule automatic

database backups to secondary storage

devices like disks,cds,tapes«.Levels of database backup:

y A full backup r dump of the database.

y Only the last modifications done to theDB.

y A backup of transaction log only



FAILURES OF DATABASE FAILURES OF DATABASE

There are many types of failures that can affect database processing. Somefailures affect the main memory only, while other involve secondary storage.Following are the types of failure:

Hardware failures

Software failures

Network failures

Media failures

Application software errors

Natural physical disasters

Carelessness

Sabotage



Types of Data Base RecoveryTypes of Data Base Recovery

There are two types data base recovery used

�Forward Recovery

�Backward Recovery



Forward ward Recovery (or Redo)Forward ward Recovery (or Redo)

It is also known as Roll Forward, when the any typeof physical damage in that situation Forward

Recovery procedure is used.

Ex;

� Crash of disk pack during writing of data to data

base.

� Or failure during flushing buffers to secondary

storage.



The data base buffers occupy an area in

the main memory. The flushing operation

can be triggered by the commit operation

of the transaction or automatically in theevent of buffers becoming full.



Recovery manager redo so that transaction·sRecovery manager redo so that transaction·s

updates to the data base.The redoing of updates to the data base.The redoing of

transaction updates is called Forwardtransaction updates is called Forward

Recovery or Roll Forward.Recovery or Roll Forward.

So, to create the lost disk due to these reason, the

system begins reading the most recent copy of the

lost data and the transaction log of the changes toit.



Continue ««««..Continue ««««..

entries from the first one that was recoded

after the copy of data base.

In this way the transaction executed byperforming in the log entries.

That is brings the lost data base copy up to

the level.



M EDIA RECOVERY

Media recovery based on storing of data when there is ahead crash on the disk .

Media recovery is based on periodically making a copy of

the data base.

In simplest form of media recovery, before system start up,the bulk copy is performed for all disks being run on

transactional system.

When the system is corrupted or lost , the system replaced

with back up disk and normal recovery process is performed.ROLL BACK

ROLL FOR WARD.

Dbms Group Presentation

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