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Which of the following scenarios may lead to an irrecoverable error in a database system ?
- a)A transaction writes a data item after it is read by an uncommitted transaction
- b)A transaction reads a data item after it is read by an uncommitted transaction
- c)A transaction reads a data item after it is written by a committed transaction
- d)A transaction reads a data item after it is written by an uncommitted transaction
Correct answer is option 'D'. Can you explain this answer?
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Which of the following scenarios may lead to an irrecoverable error in...
Option C is a normal operation. Option B is also fine as no write operation is involved. Option A can be recovered, but option D can't be. See this for an example.
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Which of the following scenarios may lead to an irrecoverable error in...
Scenario: A transaction reads a data item after it is written by an uncommitted transaction.
Explanation:
In a database system, transactions are used to perform a series of operations on the database. These operations include reading and writing data items. An irrecoverable error occurs when a transaction reads a data item that has been written by an uncommitted transaction.
Understanding Transactions:
- A transaction is a logical unit of work that is executed as a single operation.
- Transactions ensure the consistency and integrity of the database by following the ACID properties (Atomicity, Consistency, Isolation, Durability).
- ACID properties ensure that transactions are executed in a reliable and predictable manner.
Concurrent Execution of Transactions:
In a database system, multiple transactions can be executed concurrently. However, to maintain the consistency of the database, transactions need to be isolated from each other. This isolation is achieved through concurrency control mechanisms such as locking and timestamp ordering.
Scenarios:
a) A transaction writes a data item after it is read by an uncommitted transaction:
- This scenario does not lead to an irrecoverable error because the uncommitted transaction will not be able to read the data item written by the other transaction until it is committed.
- This is because the uncommitted transaction holds a lock on the data item, preventing other transactions from accessing it.
b) A transaction reads a data item after it is read by an uncommitted transaction:
- This scenario also does not lead to an irrecoverable error because the uncommitted transaction does not modify the data item.
- The transaction that reads the data item can still access the original value before it was read by the uncommitted transaction.
c) A transaction reads a data item after it is written by a committed transaction:
- This scenario does not lead to an irrecoverable error as the committed transaction has already completed.
- The transaction that reads the data item can access the updated value written by the committed transaction.
d) A transaction reads a data item after it is written by an uncommitted transaction:
- This scenario leads to an irrecoverable error because the uncommitted transaction may roll back its changes after the other transaction has read the modified value.
- This can result in inconsistent and incorrect data being read by the transaction, leading to an irrecoverable error.
Conclusion:
Out of the given scenarios, only option 'D' can lead to an irrecoverable error in a database system. It is essential to ensure proper concurrency control mechanisms and transaction isolation to prevent such errors and maintain the integrity of the database.
Explanation:
In a database system, transactions are used to perform a series of operations on the database. These operations include reading and writing data items. An irrecoverable error occurs when a transaction reads a data item that has been written by an uncommitted transaction.
Understanding Transactions:
- A transaction is a logical unit of work that is executed as a single operation.
- Transactions ensure the consistency and integrity of the database by following the ACID properties (Atomicity, Consistency, Isolation, Durability).
- ACID properties ensure that transactions are executed in a reliable and predictable manner.
Concurrent Execution of Transactions:
In a database system, multiple transactions can be executed concurrently. However, to maintain the consistency of the database, transactions need to be isolated from each other. This isolation is achieved through concurrency control mechanisms such as locking and timestamp ordering.
Scenarios:
a) A transaction writes a data item after it is read by an uncommitted transaction:
- This scenario does not lead to an irrecoverable error because the uncommitted transaction will not be able to read the data item written by the other transaction until it is committed.
- This is because the uncommitted transaction holds a lock on the data item, preventing other transactions from accessing it.
b) A transaction reads a data item after it is read by an uncommitted transaction:
- This scenario also does not lead to an irrecoverable error because the uncommitted transaction does not modify the data item.
- The transaction that reads the data item can still access the original value before it was read by the uncommitted transaction.
c) A transaction reads a data item after it is written by a committed transaction:
- This scenario does not lead to an irrecoverable error as the committed transaction has already completed.
- The transaction that reads the data item can access the updated value written by the committed transaction.
d) A transaction reads a data item after it is written by an uncommitted transaction:
- This scenario leads to an irrecoverable error because the uncommitted transaction may roll back its changes after the other transaction has read the modified value.
- This can result in inconsistent and incorrect data being read by the transaction, leading to an irrecoverable error.
Conclusion:
Out of the given scenarios, only option 'D' can lead to an irrecoverable error in a database system. It is essential to ensure proper concurrency control mechanisms and transaction isolation to prevent such errors and maintain the integrity of the database.
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Which of the following scenarios may lead to an irrecoverable error in a database system ?a)A transaction writes a data item after it is read by an uncommitted transactionb)A transaction reads a data item after it is read by an uncommitted transactionc)A transaction reads a data item after it is written by a committed transactiond)A transaction reads a data item after it is written by an uncommitted transactionCorrect answer is option 'D'. Can you explain this answer?
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