Question 1

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

Accepted Answer

In a page-level lock, the DBMS will lock an entire disk page to ensure data consistency and prevent conflicts between transactions accessing the same page. Other transactions that need to access the same page must wait until the lock is released.

Question 2

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

Accepted Answer

A scheduler is responsible for ensuring data isolation and concurrency control by managing access to shared data among concurrent transactions. This ensures that transactions do not interfere with each other and that the final database state is consistent.

Question 3

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

Accepted Answer

Incomplete or improper transactions can leave the database in an inconsistent state, impacting data accuracy and reliability. As a result, it is essential to maintain transactional integrity to ensure that data is consistently accurate and reliable.

Question 4

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, not multiple transactions simultaneously.

Question 5

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 6

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 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 it involves stopping and rescheduling transactions, which can consume significant CPU and memory resources.

Question 8

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

Accepted Answer

The scheduler is responsible for determining the order in which the operations within concurrent transactions are executed. This is necessary to ensure data consistency and prevent conflicts between concurrent transactions.

Question 9

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 10

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 11

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 12

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 13

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 14

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 statement is true. Uncommitted data is a violation of the isolation property of transactions in database systems. When two transactions are executed concurrently and the first transaction is rolled back after the second transaction has already accessed the uncommitted data, it can lead to inconsistent or incorrect results in the database. To prevent this, database systems use locking mechanisms and isolation levels to ensure proper transactional behavior.

Question 15

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 16

An optimistic approach is based on the assumption that the majority of the database operations do not conflict.

Accepted Answer

An optimistic approach assumes that conflicts are rare and that transactions will be completed without interference from other transactions.

Question 17

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 cannot ensure semantic correctness of transactions as it is dependent on the end user or programmer who defines them.

Question 18

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 DBMS must implement controls to ensure that multiple transactions are executed in a way that maintains the consistency and integrity of the database. To achieve this, the DBMS must enforce serializability, which ensures that the transactions are executed as if they were executed one at a time in a specific order, and isolation, which prevents one transaction from seeing the uncommitted changes made by another transaction. Additionally, the DBMS must also support atomicity and durability to ensure that transactions are executed completely or not at all, and that changes made by committed transactions are permanently stored in the database, respectively.

Question 19

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 is true. A field-level lock only locks specific fields within a row, allowing other transactions to access the remaining fields as long as they are not locked. This allows for better concurrency when multiple transactions only need to access different fields within the same row.

Question 20

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 how optimistic concurrency control works during the read phase. The transaction reads the database, performs computations, and updates a private copy of the values.

Quiz 10: Transaction Management and Concurrency Control