35 Questions
What are the three closely related functions intended to ensure database reliability and consistency?
Transaction support, concurrency control services, and recovery services
What is the process of restoring the database to a correct state following a failure?
Database recovery
What is a Transaction in the context of database management?
An action carried out by a single user or application program that reads or updates the contents of the database
What is the purpose of a concurrency control protocol in a DBMS?
Prevents database accesses from interfering with one another
What does database recovery aim to achieve in the event of a failure?
Restore the database to a consistent state
What is a schedule in the context of transaction management?
A sequence of operations by concurrent transactions preserving individual transaction order
Why is the order of read and write operations crucial for serializability?
It affects the ability to maintain consistency and avoid interference between transactions
What is used to test for conflict serializability?
Precedence graph
What is the purpose of recoverability in transaction management?
To examine the ability to undo transaction effects and maintain changes after commit
What does locking ensure in concurrent transactions?
The serializability of concurrent transactions
What is the main objective of developing a database in the context of concurrency control?
To enable many users to access shared data concurrently
Which problem occurs when a transaction reads values from the database and another transaction updates some of them, leading to inaccurate results?
Inconsistent analysis problem
What is the main aim of concurrency control protocols?
To schedule transactions to avoid interference and prevent problems
What is the significance of interleaved operations of transactions in achieving concurrent execution?
It helps achieve concurrent execution and improve throughput
What is the lost update problem in the context of concurrency control?
When one user's update operation is overridden by another user
What is the purpose of the recovery manager in database architecture?
To restore the database to a consistent state after a failure
What are the ACID properties that all transactions should possess?
Atomicity, Consistency, Isolation, and Durability
What is the role of concurrency control in database management?
Managing simultaneous operations on the database without interference
What is the primary purpose of exclusive locks in transaction management?
Preventing both read and update access by other transactions
What happens to committed transactions in a database?
They cannot be aborted and result in reaching a new consistent state
In two-phase locking (2PL) protocol, what is the purpose of the shrinking phase?
Releasing locks without acquiring new ones
What is the primary function of the transaction manager in database architecture?
To coordinate transactions
What is the potential consequence of a transaction causing a series of rollbacks known as cascading rollback?
Inconsistent database state
How can lock contention manifest in index structures?
Frequent access leading to conflicts at higher levels of trees
When are locks explicitly released in transaction management?
During execution or when the transaction terminates
What is the purpose of two-phase locking (2PL) protocol?
To acquire locks in a growing phase and release locks in a shrinking phase
What is the consequence of a single transaction causing a series of rollbacks?
Cascading rollback
How is lock contention managed in index structures?
By treating each index page as a data item and applying the two-phase locking protocol
What is the potential consequence of being unable to acquire new locks during lock upgrade or downgrade?
Livelock
What must transactions do before accessing data items?
Lock the data items explicitly
What is the purpose of the growing phase in the two-phase locking (2PL) protocol?
To acquire locks for data items
What is the primary function of shared locks in transaction management?
Allow reading but not updating of a data item
What does the shrinking phase in two-phase locking (2PL) protocol involve?
Releasing locks for data items
What is the potential consequence of failing to acquire new locks during lock upgrade or downgrade?
Livelock occurrence
How can concurrency control be managed for index structures?
Treating each index page as a data item and applying the two-phase locking protocol
Study Notes
Transaction Management and Locking Protocols
- Locks prevent other transactions from modifying or reading a data item, with exclusive locks providing both read and update access.
- Shared locks allow reading but not updating of a data item, and the size of the item determines the granularity of the lock.
- More than one transaction can hold shared locks, but exclusive locks give exclusive access to the item.
- Transactions must lock data items before accessing them, and locks must be explicitly released during or after the transaction.
- Two-phase locking (2PL) protocol involves a growing phase for acquiring locks and a shrinking phase for releasing locks, with no new locks acquired after release.
- A single transaction causing a series of rollbacks is called cascading rollback, which can be prevented with rigorous 2PL or strict 2PL.
- Deadlock can occur with two-phase locking, requiring a deadlock detection and recovery scheme.
- Concurrency control for index structures can be managed by treating each index page as a data item and applying the two-phase locking protocol.
- Lock contention may occur with index structures due to frequent access, particularly at higher levels of trees.
- Transactions can upgrade or downgrade locks, with the possibility of livelock if unable to acquire new locks.
- Locks are used to request shared or exclusive access to data items, and any transaction that needs to access a data item must first lock it.
- Locks are released explicitly during execution or when the transaction terminates, and some systems permit lock upgrades or downgrades.
Transaction Management and Locking Protocols
- Locks prevent other transactions from modifying or reading a data item, with exclusive locks providing both read and update access.
- Shared locks allow reading but not updating of a data item, and the size of the item determines the granularity of the lock.
- More than one transaction can hold shared locks, but exclusive locks give exclusive access to the item.
- Transactions must lock data items before accessing them, and locks must be explicitly released during or after the transaction.
- Two-phase locking (2PL) protocol involves a growing phase for acquiring locks and a shrinking phase for releasing locks, with no new locks acquired after release.
- A single transaction causing a series of rollbacks is called cascading rollback, which can be prevented with rigorous 2PL or strict 2PL.
- Deadlock can occur with two-phase locking, requiring a deadlock detection and recovery scheme.
- Concurrency control for index structures can be managed by treating each index page as a data item and applying the two-phase locking protocol.
- Lock contention may occur with index structures due to frequent access, particularly at higher levels of trees.
- Transactions can upgrade or downgrade locks, with the possibility of livelock if unable to acquire new locks.
- Locks are used to request shared or exclusive access to data items, and any transaction that needs to access a data item must first lock it.
- Locks are released explicitly during execution or when the transaction terminates, and some systems permit lock upgrades or downgrades.
Transaction Management and Locking Protocols
- Locks prevent other transactions from modifying or reading a data item, with exclusive locks providing both read and update access.
- Shared locks allow reading but not updating of a data item, and the size of the item determines the granularity of the lock.
- More than one transaction can hold shared locks, but exclusive locks give exclusive access to the item.
- Transactions must lock data items before accessing them, and locks must be explicitly released during or after the transaction.
- Two-phase locking (2PL) protocol involves a growing phase for acquiring locks and a shrinking phase for releasing locks, with no new locks acquired after release.
- A single transaction causing a series of rollbacks is called cascading rollback, which can be prevented with rigorous 2PL or strict 2PL.
- Deadlock can occur with two-phase locking, requiring a deadlock detection and recovery scheme.
- Concurrency control for index structures can be managed by treating each index page as a data item and applying the two-phase locking protocol.
- Lock contention may occur with index structures due to frequent access, particularly at higher levels of trees.
- Transactions can upgrade or downgrade locks, with the possibility of livelock if unable to acquire new locks.
- Locks are used to request shared or exclusive access to data items, and any transaction that needs to access a data item must first lock it.
- Locks are released explicitly during execution or when the transaction terminates, and some systems permit lock upgrades or downgrades.
Test your knowledge of managing simultaneous operations on a database without interference. Explore the need for concurrency control and the challenges of enabling multiple users to access shared data concurrently.
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