Skip to main content
UploadLanguage (EN)Support
BusinessMobileSocial MediaMarketingTechnologyArt & PhotosCareerDesignEducationPresentations & Public SpeakingGovernment & NonprofitHealthcareInternetLawLeadership & ManagementAutomotiveEngineeringSoftwareRecruiting & HRRetailSalesServicesScienceSmall Business & EntrepreneurshipFoodEnvironmentEconomy & FinanceData & AnalyticsInvestor RelationsSportsSpiritualNews & PoliticsTravelSelf ImprovementReal EstateEntertainment & HumorHealth & MedicineDevices & HardwareLifestyle
Uploaded bySangeethaSasi1
PPTX, PDF25 views

Hema rdbms

A transaction is a logical unit of work that maintains the ACID properties of atomicity, consistency, isolation, and durability. It can consist of one or more SQL commands or portions of an application program. Transactions must be atomic, leaving the database in a consistent state whether the transaction commits or aborts. Isolation ensures that transactions appear to execute sequentially despite concurrent execution. The database system guarantees transaction durability even in the event of failures.

Education◦
Download to read offline
S.AZHAGARAMMAL MSc(IT) Nadar Saraswathi College of Arts and Science, Theni.
A transaction can be defined as a logical unit of work on the database. This may be an entire program, a piece of a program or a single command (like the SQL commands such as INSERT or UPDATE) and it may engage in any number of operations on the database. In the database context, the execution of an application program can be thought of as one or more transactions with non-database processing taking place in between.
A transaction is a very small unit of a program and it may contain several lowlevel tasks. 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. ACID properties and its concepts of a transaction are put forwarded by Haerder and Reuter in the year 1983.
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.
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.
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.
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.
When multiple transactions are being executed by the operating system in a multiprogramming environment, there are possibilities that instructions of one transactions are interleaved with some other transaction. Schedule − A chronological execution sequence of a transaction is called a schedule. A schedule can have many transactions in it, each comprising of a number of instructions/tasks.
It is a schedule in which transactions are aligned in such a way that one transaction is executed first. When the first transaction completes its cycle, then the next transaction is executed. Transactions are ordered one after the other. This type of schedule is called a serial schedule, as transactions are executed in a serial manner.
Active − In this state, the transaction is being executed. This is the initial state of every transaction. Partially Committed − When a transaction executes its final operation, it is said to be in a partially committed state. Failed − A transaction is said to be in a failed state if any of the checks made by the database recovery system fails. A failed transaction can no longer proceed further.
Aborted − If any of the checks fails and the transaction has reached a failed state, then the recovery manager rolls back all its write operations on the database to bring the database back to its original state where it was prior to the execution of the transaction. Transactions in this state are called aborted. Committed − If a transaction executes all its operations successfully, it is said to be committed. All its effects are now permanently established on the database system.
1.Read your account balance 2. Deduct the amount from your balance 3. Write the remaining balance to your account 4. Read your friend’s account balance 5. Add the amount to his account balance 6. Write the new updated balance to his account