TCL UNIT 5

What are the potential problems when a DBMS executes multiple transactions concurrently?

• Phantom problem

• The dirty read problem

• Unrepeatable read problem

• All of the above

Which of the following schemas are used for ensuring atomicity?

• ACID properties and transactions

• Data redundancy management

• Normalization techniques

• CAPM principles

Assume transaction A holds a shared lock R. If transaction B also requests for a shared lock on

R, it will:

• result in deadlocked situation

• immediately be granted

• immediately be rejected

• be grateful as soon as it released by A

Consider the following schedules involving 2 transactions which one of the following

statements are true?

S1: r1(X); r1(Y); r2(X); r2(Y); w2(Y); w1(X)

S2: r1(X); r2(X); r2(Y); w2(Y); r1(Y); w1(X)

• Both S1 and S2 are conflicted serializable

• S1 is conflict serializable and S2 is conflict serializable

• S1 is not conflict serializable and S2 is conflict serializable

• Both S1 and S2 are not conflict serializable

Which of the following scenarios may lead to an irrecoverable error in database system?

• A transaction writes a data item after it is read by an uncommitted transaction

• A transaction read a data item after it is read by an uncommitted transaction

• A transaction read a data item after it is written by an uncommitted transaction

• A transaction read a data item after it is written by a committed transaction

Which of the following concurrency control protocol ensures both conflict serializability

and freedom from deadlock?

(i) 2 phase locking
(ii) time stamp ordering

• (i) only

• (ii) only

• None of these

• (i) and (ii)

In case of time stamp ordering R-timestamp (Q) denotes

• the largest timestamp of any transaction that execute read(Q) successfully

• the average timestamp of any transaction that execute read(Q) successfully

• the average time stamp of any transaction that execute read(Q) unsuccessfully

• the smallest timestamp of any transaction that execute read(Q) successfully

Consider the following transactions with data items P and Q initialized to ‘0’

T1: read (P);

Read (Q);

if P=0, then Q= Q+1

write (Q);

T2: read (Q)

Read (P)

if Q=0, then P= P+1;

write (P);

Any non-serial interleaving of T1 and T2 for concurrent execution leads to:

• a serializable schedule

• a schedule that is not conflict serializable

• a conflict serializable schedule

• a schedule for which precedence graph cannot be drawn

In the context of transaction management, what does the term 'Durability' mean?

• Transactions can be reversed at any time.

• Transactions are only temporarily stored in the database.

• Changes made by committed transactions are permanent and cannot be undone.

• Transactions must be processed within a short duration.

What happens when a transaction holds an exclusive lock on a data item and another transaction requests a shared lock on the same item?

• It will be granted immediately

• It will be queued until the exclusive lock is released

• It will result in a deadlock

• It will be rejected outright