16 Questions
What happens if a machine crashes between subtracting money from a savings account and adding it to a checking account?
The money is lost
Why is it necessary to perform addition to checking first in a transaction?
To ensure the bank doesn't lose money
What is the state of a transaction when it starts its operation?
Active
What is a transaction in the context of database systems?
A set of changes that must be made together
What can cause a transaction to fail?
Several reasons including computer failure, transaction errors, and concurrency control enforcement
What happens when a transaction is rolled back?
The database is restored to its previous state
What is the state of a transaction when it is successfully completed?
Committed
What can cause a disk failure during a transaction?
A disk read/write head crash
A transaction processing must ensure that the database is in a consistent state after its execution. What property of a transaction ensures this?
Atomicity
What is the purpose of the read_item(X) operation?
Reads a database item into a program variable
What is the minimum number of database access operations in a transaction?
One
What happens to the database if a transaction is aborted?
The database remains consistent
What is the purpose of the write_item(X) operation?
Writes the value of a program variable into the database item
What is the benefit of atomicity in transaction processing?
Improved data consistency
What is an example of a transaction in a banking system?
Transferring money from a savings account to a checking account
What are the basic operations on a database?
Read and write
Study Notes
Transaction Processing
- A transaction is a logical unit of work that includes one or more database access operations, such as retrieval, insertion, deletion, and modification.
Characteristics of a Transaction
- A transaction must be either completed or aborted.
- A transaction is a program unit whose execution may change the contents of a database.
- To ensure the integrity of the database, a transaction must be atomic (also called serialisability).
Atomic Transaction
- An atomic transaction is a transaction in which either all actions associated with the transaction are executed to completion or none are performed.
Basic Operations on Database
- Read and write are the basic operations on a database.
-
read_item(X)reads a database item named X into a program variable. -
write_item(X)writes the value of program variable X into the database item named X.
Example of a Transaction
- A customer transfers Rs. 1000 from savings to a checking account using an ATM.
- The transaction requires two steps: subtracting the money from the savings account balance and adding the money to the checking account balance.
Reasons for a Transaction to Fail
- Computer failure: hardware, software, or network error occurs in the computer system during transaction execution.
- Transaction or system error: an operation in the transaction may cause it to fail, such as integer overflow or division by 0.
- Local errors or exception conditions: certain conditions may occur during transaction execution, such as insufficient account balance.
- Concurrency control enforcement: a transaction may be aborted due to a deadlock.
- Disk failure: disk blocks may lose their data due to a disk read/write head crash.
- Physical problems and catastrophes: fire, theft, etc.
States of a Transaction
- Active state: after the transaction starts its operation.
- Partially committed: when the last state is reached.
- Aborted: after the transaction has been rolled back and the database has been restored to its state prior to the start of the transaction.
- Committed: after successful completion of the transaction.
This quiz covers the concept of transactions in database management systems, including characteristics and atomicity. Test your knowledge of database transactions and their properties.
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