Snapshot Isolation - DBMS Questions and Answers

1.

Each of a pair of transactions has read data that is written by the other, but there is no data written by both transactions, is referred to as

   A.) Read skew
   B.) Update skew
   C.) Write lock
   D.) None of the mentioned

Answer: Option 'D'

None of the mentioned

2.

Under first updater wins the system uses a __________ mechanism that applies only to updates.

   A.) Beat
   B.) Locking
   C.) Read
   D.) Close

Answer: Option 'B'

Locking
Reads are unaffected by this, since they do not obtain locks.

3.

Snapshot isolation is used to give

   A.) Transaction a snapshot of the database
   B.) Database a snapshot of the transaction
   C.) Database a snapshot of committed values in the transaction
   D.) Transaction a snapshot of the database and Database a snapshot of committed values in the transaction

Answer: Option 'D'

Transaction a snapshot of the database and Database a snapshot of committed values in the transaction

4.

When a transaction Ti attempts to update a data item, it requests a _________ on that data item.

   A.) Read lock
   B.) Update lock
   C.) Write lock
   D.) Chain lock

Answer: Option 'C'

Reads are unaffected by this, since they do not obtain locks.

5.

Evaluate the following CREATE SEQUENCE statement:

CREATE SEQUENCE seq1
START WITH 100
INCREMENT BY 10
MAXVALUE 200
CYCLE
NOCACHE;

The sequence SEQ1 has generated numbers up to the maximum limit of 200. You issue the following SQL statement:
SELECT seq1.nextval FROM dual;
What is displayed by the SELECT statement?

   A.) 1
   B.) 10
   C.) 100
   D.) an error

Answer: Option 'A'

Sequence is used to generate a series of values.

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