unit no 5 transaction PROCESSING in dbms

1. UNIT NO 5
TRANSACTION
PROCESSING
ARVIND S. SARDAR

2. TRANSACTION
TRANSACTION CONCEPT
• A transaction can be defined as a group of tasks.
• A single task is the minimum processing unit which cannot be divided further.
• Let’s take an example of a simple transaction.
• Transactions access data using read and write operations.

3. TRANSACTION
• Suppose a bank employee transfers Rs 500 from A's account to B's account. This very
simple and small transaction involves several low-level tasks.
• A’s Account
• Open_Account(A)
• Old_Balance = A.balance
• New_Balance = Old_Balance – 500
• A.balance = New_Balance Close_Account(A)
B’s Account
Open_Account(B)
Old_Balance = B.balance
New_Balance = Old_Balance + 500
B.balance = New_Balance Close_Account(B)

4. TRANSACTION PROPERTY
ACID Properties
• A transaction in a database system must maintain Atomicity, Consistency, Isolation,
and Durability − commonly known as ACID properties − in order to ensure accuracy,
completeness, and data integrity.
• Atomicity − This property states that a transaction must be treated as an atomic unit,
that is, either all of its operations are executed or none. There must be no state in a
database where a transaction is left partially completed. States should be defined either
before the execution of the transaction or after the execution/abortion/failure of the
transaction.
• Consistency − The database must remain in a consistent state after any transaction. No
transaction should have any adverse effect on the data residing in the database. If the
database was in a consistent state before the execution of a transaction, it must remain
consistent after the execution of the transaction as well.

5. TRANSACTION
• Durability − The database should be durable enough to hold all its
latest updates even if the system fails or restarts. If a transaction updates
a chunk of data in a database and commits, then the database will hold
the modified data. If a transaction commits but the system fails before
the data could be written on to the disk, then that data will be updated
once the system springs back into action.
• Isolation − In a database system where more than one transaction are
being executed simultaneously and in parallel, the property of isolation
states that all the transactions will be carried out and executed as if it is
the only transaction in the system. No transaction will affect the
existence of any other transaction.

6. TRANSACTION
Atomicity: A transaction is an atomic unit of processing, and it either has to
be performed in its entirety or not at all.
Consistency: A successful execution of a transaction must take a consistent
database state to a (new) consistent database state. (integrity constraints)
Isolation: A transaction must not make its modifications visible to other
transactions until it is committed, i.e., each transaction is unaware of other
transactions executing concurrently in the system. ( concurrency control)
Durability: Once a transaction has committed its changes, these changes
must never get lost due to subsequent (system) failures. ( recovery)

8. States of Transactions
• A transaction in a database can be in one of the following states −

9. States of Transactions

10. States of Transactions
1. Active State-
• This is the first state in the life cycle of a transaction.
• A transaction is called in an active state as long as its instructions are getting
executed.
• All the changes made by the transaction now are stored in the buffer in main
memory.
2. Partially Committed State-
• After the last instruction of transaction has executed, it enters into a partially
committed state.
• After entering this state, the transaction is considered to be partially committed.
• It is not considered fully committed because all the changes made by the transaction
are still stored in the buffer in main memory.

11. States of Transactions
3. Committed State-
• After all the changes made by the transaction have been successfully stored into the
database, it enters into a committed state.
• Now, the transaction is considered to be fully committe
4. Failed State-
• When a transaction is getting executed in the active state or partially committed state and
some failure occurs due to which it becomes impossible to continue the execution, it
enters into a failed state.

12. States of Transactions
5. Aborted State-
• After the transaction has failed and entered into a failed state, all the
changes made by it have to be undone.
• To undo the changes made by the transaction, it becomes necessary to roll
back the transaction.
• After the transaction has rolled back completely, it enters into an aborted
state

13. DATABASE BACKUP
• Database backup is the process of backing up the operational state, architecture
and stored data of database software.
Types of Failure
Failures may be
• Transaction: Caused by errors within the transaction processes.
• System: Caused by failure of network or operating system
• Media: Failure of hard disk, out of memory errors, out of disk space errors.
• Human error
• Software failure
• Hardware failure

14. Causes of failure

15. TYPES OF DATABASE BACKUP
There are more than ten different types of data backup
Full backup
A full backup is when every single file and folder in the system is backed up.
A full backup takes longer and requires more space than other types of
backups but the process of restoring lost data from backup is much faster.
Incremental backup
With incremental backup, only the initial backup is a full one. Subsequent
backups only stores changes that were made since the previous backup.
The process of restoring lost data from backup is longer but the backup
process is much quicker.

16. TYPES OF DATABASE BACKUP
Differential backup
Differential backup is similar to incremental backup. With both, the initial backup is full
and subsequent backups only store changes made to files since the last backup. This
type of backup requires more storage space than incremental backup does, however, but it
also allows for a faster restore time.
Mirror backup
A mirror backup, as the name implies, is when an exact copy is made of the source data. The
advantage of mirror backup as opposed to full, incremental, or differential backups, is that you’re
not storing old, obsolete files.
When obsolete files are deleted, they disappear from the mirror backup as well when the system
backs up. The downside to mirror backup is that if files are accidentally deleted, they can be lost
from the backup is well if the deletion isn’t discovered before the next scheduled backup.

17. TYPES OF DATABASE BACKUP
• Physical Backup
• Logical Backup

18. TYPES OF DATABASE BACKUP

19. TYPES OF DATABASE BACKUP
Physical Files, such as text files, are stored as a single
document on your hard drive. These files can easily be backed
up just like any other files on your system.
Logical Data Elements such as tables, records and their
associated meta data are stored across many different
locations. Backups for tables and other logical database
elements usually require special tools that are designed to
work with your specific database platforms.

20. DATABASE RECOVERY
• Database recovery means recovering the data when it get deleted, hacked or
damaged accidentally.
• Recovery is the process of restoring a database to the correct state in the
event of a failure.
• It ensures that the database is reliable and remains in consistent state in
case of a failure.
• To restore a physical backup of a data file or control file is to reconstruct it
and make it available to the database server.

21. DATABASE RECOVERY
Database recovery can be classified into two parts;
1. Rolling Forward applies redo records to the corresponding data
blocks. After the roll forward, any changes that were not
committed must be undone.
2. Rolling Back applies rollback segments to the data files. It is
stored in transaction tables.

22. DATABASE RECOVERY
Basic Recovery Steps: Rolling Forward and Rolling Back"