MCQ1 mark
Consider concurrent execution of two transactions and in a DBMS, both of which access a data object . For these two transactions to not conflict on , which one of the following statements must be true?
Single correct
MCQ1 mark
A schedule of three database transactions , , and is shown. and denote read and write of data item by transaction , . The transaction aborts at the end. Which other transaction(s) will be required to be rolled back?
Single correct
MSQ1 mark
An audit of a banking transactions system has found that on an earlier occasion, two joint holders of account attempted simultaneous transfers of Rs. 10000 each from account to account . Both transactions read the same value, Rs. 11000, as the initial balance in and were allowed to go through. was credited Rs. 10000 twice. was debited only once and ended up with a balance of Rs. 1000.
Which of the following properties is/are certain to have been violated by the system?
One or more correct
MSQ2 marks
Consider the database transactions T1 and T2, and data items X and Y. Which of the schedule(s) is/are conflict serializable?
Transaction T1 Transaction T2
R1(X) W2(X)
W1(Y) W2(Y)
R1(X) COMMIT(T2)
W1(X)
COMMIT(T1)One or more correct
MSQ2 marks
Consider the following read-write schedule over three transactions , , and , where the subscripts in the schedule indicate transaction IDs:
Which of the following transaction schedules is/are conflict equivalent to ?
One or more correct
MCQ1 mark
Once the DBMS informs the user that a transaction has been successfully completed, its effect should persist even if the system crashes before all its changes are reflected on disk. This property is called
Single correct
MSQ1 mark
Which of the following statements about the Two Phase Locking (2PL) protocol is/are TRUE?
One or more correct
MCQ2 marks
Let and denote read and write operations on a data element by a transaction , respectively. Consider the schedule with four transactions.
Which one of the following serial schedules is conflict equivalent to ?
Single correct
Answer key coming soon
MSQ1 mark
Suppose a database system crashes again while recovering from a previous crash. Assume checkpointing is not done by the database either during the transactions or during recovery.
Which of the following statements is/are correct?
One or more correct
Answer key coming soon
MCQ2 marks
Let and denote read and write operations respectively on a data item by a transaction . Consider the following two schedules.
Which one of the following options is correct?
Single correct
Answer key coming soon
MCQ2 marks
Let S be the following schedule of operations of three transactions , and in a relational database system:
Consider the statements P and Q below:
P: S is conflict-serializable.
Q: If commits before finishes, then S is recoverable.
Which one of the following choices is correct?
Single correct
Answer key coming soon
MCQ2 marks
Consider a schedule of transactions and (the first table in the figure).
Here, RX stands for "Read(X)" and WX stands for "Write(X)". Which one of the following schedules is conflict equivalent to the above schedule?
The four candidate schedules (A) to (D) are shown in the figure.
Single correct
Answer key coming soon
MCQ1 mark
Consider the following two statements about database transaction schedules:
I. Strict two-phase locking protocol generates conflict serializable schedules that are also recoverable.
II. Timestamp-ordering concurrency control protocol with Thomas' Write Rule can generate view serializable schedules that are not conflict serializable.
Which of the above statements is/are TRUE?
Single correct
MCQ2 marks
In a database system, unique timestamps are assigned to each transaction using Lamport's logical clock. Let and be the timestamps of transactions and respectively. Besides, holds a lock on the resource R, and has requested a conflicting lock on the same resource R. The following algorithm is used to prevent deadlocks in the database system assuming that a killed transaction is restarted with the same timestamp.
if then
is killed
else waits.
Assume any transaction that is not killed terminates eventually. Which of the following is TRUE about the database system that uses the above algorithm to prevent deadlocks?
Single correct
Answer key coming soon
NAT2 marks
Two transactions and are given as
where denotes a *read* operation by transaction on a variable and denotes a *write* operation by transaction on a variable . The total number of conflict serializable schedules that can be formed by and is ________.
Numerical answer
Answer key coming soon
MCQ1 mark
Which one of the following is NOT a part of the ACID properties of database transactions?
Single correct
Answer key coming soon
MCQ2 marks
Consider the following two phase locking protocol. Suppose a transaction accesses (for read or write operations), a certain set of objects . This is done in the following manner:
Step 1. acquires exclusive locks to in increasing order of their addresses.
Step 2. The required operations are performed.
Step 3. All locks are released.
This protocol will
Single correct
Answer key coming soon
MCQ1 mark
Suppose a database schedule involves transactions . Construct the precedence graph of with vertices representing the transactions and edges representing the conflicts. If is serializable, which one of the following orderings of the vertices of the precedence graph is guaranteed to yield a serial schedule?
Single correct
Answer key coming soon
MCQ2 marks
Consider the following database schedule with two transactions, and .
where denotes a *read* operation by transaction on a variable , denotes a *write* operation by on a variable and denotes an *abort* by transaction .
Which one of the following statements about the above schedule is TRUE?
Single correct
Answer key coming soon
MCQ1 mark
Consider the following transaction involving two bank accounts x and y.
read(x); x := x - 50; write(x); read(y); y:= y + 50; write(y)
The constraint that the sum of the accounts x and y should remain constant is that ofSingle correct
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