Question 1

In a page-level lock, the DBMS will lock an entire diskpage.

Accepted Answer

In page-level locking, the DBMS locks an entire disk page rather than individual records or fields within the page.

Question 2

Most real-world database transactions are formed by only one database request.

Accepted Answer

Most real-world database transactions consist of multiple database requests to ensure data integrity and consistency across complex operations.

Question 3

Timestamps must only have the single property of uniqueness.

Accepted Answer

Time stamps must not only be unique but also accurately represent a specific point in time, ensuring both uniqueness and temporal accuracy.

Question 4

A scheduler facilitates data isolation to ensure that two transactions do not update the same data element at the same time.

Accepted Answer

This is true. The scheduler plays a crucial role in ensuring data isolation by allowing only one transaction to access a data element at a time. This prevents conflicts and ensures that the data remains consistent.

Question 5

A growing phase in a two-phase lock is when a transaction acquires all the required locks without locking any data.

Accepted Answer

In the growing phase of a two-phase locking protocol, a transaction can acquire locks but cannot release any locks. It does not mean it acquires locks without locking any data; rather, it actively locks data items it needs to access or modify.

Question 6

The phenomenon of uncommitted data occurs when two transactions are executed concurrently and the first transaction is rolled back after the second transaction has already accessed the uncommitted data-thus violating the isolation property of transactions.

Accepted Answer

This is true. Uncommitted data refers to data that has been modified by a transaction but not yet committed. If another transaction attempts to access this data before the first transaction has committed, it can lead to inconsistency and violate the transaction's isolation property. If the first transaction is subsequently rolled back, any modifications it made to the uncommitted data will be lost, violating the atomicity property of transactions as well.

Question 7

Time stamping demands a lot of system resources because many transactions might have to be stopped, rescheduled, and stamped.

Accepted Answer

Time stamping requires a lot of system resources because every transaction has to be evaluated and given a timestamp, which can cause delays and require the rescheduling of transactions. This process can demand a lot of resources from the system.

Question 8

Durability requires that all portions of the transaction must be treated as a single, logical unit of work in which all operations are applied and completed to produce a consistent database.

Accepted Answer

Durability refers to the guarantee that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors. The concept described in the question actually defines atomicity, not durability.

Question 9

The multiuser DBMS must implement controls to ensure serializability and isolation of transactions, in addition to atomicity and durability, in order to guard the database's consistency and integrity.

Accepted Answer

The statement is true. Multiuser DBMSs must implement various controls such as locking, concurrency control, and transaction management to ensure that multiple transactions do not interfere with each other and the database remains consistent and free from any anomalies. Atomicity and durability are also necessary properties of a reliable DBMS.

Question 10

Serializability means that data used during the execution of a transaction cannot be used by a second transaction until the first one is completed.

Accepted Answer

Serializability refers to the concept in database management systems where a schedule (sequence of transactions) is considered serializable if its outcome is equivalent to one that could have been obtained by executing all transactions serially, i.e., one after the other, without any overlapping in time. It does not specifically mean that data used during the execution of a transaction cannot be used by a second transaction until the first one is completed; rather, it focuses on ensuring that concurrent transactions yield results consistent with some order of serial execution.

Question 11

The DBMS guarantees that the semantic meaning of a transaction truly represents the real-world event.

Accepted Answer

The DBMS does not guarantee the semantic meaning of a transaction. It only ensures the consistency and durability of the data. It is the responsibility of the application developer and database designer to ensure that the transaction accurately represents the real-world events.

Question 12

The scheduler establishes the order in which the operations within concurrent transactions are executed.

Accepted Answer

The scheduler is responsible for defining the order in which the operations of concurrent transactions are executed to ensure consistency and avoid conflicts.

Question 13

A shared lock produces no conflict as long as all the concurrent transactions are read-write only.

Accepted Answer

A shared lock is designed for read-only operations, allowing multiple transactions to read a resource without conflict. However, if any transaction attempts to write, it conflicts with shared locks, necessitating exclusive locks for write operations.

Question 14

To ensure consistency of the database, every transaction must begin with the database in an unstable state.

Accepted Answer

Every transaction must begin with the database in a consistent state, not an unstable state. A consistent state means that there are no violations of the database's constraints or rules. Transactions are used to maintain this consistency and update the database in a way that still satisfies the constraints and rules.

Question 15

Atomicity indicates the permanence of the database's consistent state.

Accepted Answer

Atomicity, in database systems, refers to the principle that database transactions are either fully completed or not done at all, ensuring that the database remains in a consistent state throughout each transaction. It does not directly indicate the permanence of the database's consistent state.

Question 16

A field-level lock allows concurrent transactions to access the same row, as long as they require the use of different fields within that row.

Accepted Answer

This statement is true. A field-level lock only locks the specific field within a row, allowing other transactions to access the row as long as they do not need to use the same locked field. This allows for more concurrency and prevents unnecessary blocking.

Question 17

When using an optimistic approach, during the read phase, a transaction reads the database, executes the needed computations, and makes the updates to a private copy of the database values.

Accepted Answer

This is the basic idea of optimistic concurrency control. The transaction assumes that there will be no conflicts and executes as if it has exclusive access to the database. However, before committing, the transaction checks if any other transactions have modified the same data, and if so, it aborts and restarts.

Question 18

Incomplete or improper transactions can have a devastating effect on database integrity.

Accepted Answer

Incomplete or improper transactions can cause inconsistencies in the data, leading to poor database integrity. For example, if a transaction fails to update one field in a record, but updates all other fields, it can result in incomplete or erroneous data that can affect other operations and compromise the overall integrity of the database. Therefore, it is important to ensure that all transactions are executed properly and completely to maintain database integrity.

Question 19

A lock guarantees the open use of a data item to multiple transactions.

Accepted Answer

A lock restricts the access of a data item to a single transaction at a time, ensuring data consistency and integrity. Therefore, a lock does not guarantee open use of a data item to multiple transactions.

Question 20

Although the DBMS is designed to recover a database to a previous consistent state when an interruption prevents the completion of a required set of transactions, the transactions themselves are defined by the end user or programmer and must be semantically correct.

Accepted Answer

The DBMS can only ensure consistency and recoverability based on the transactions that are executed by the end user or programmer. If the transactions themselves are not semantically correct, the DBMS cannot prevent data inconsistencies or guarantee successful recovery.

Quiz 10: Transaction Management and Concurrency Control