The concept of locking can be used to solve the problem of
1. Lost update
2. Uncommitted dependency
3. Inconsistent data
The concept of locking can be used to solve the problem of lost update, uncommitted dependency and prevents inconsistency among data but it is not capable of preventing the deadlock always.
What are the potential problems when a DBMS executes multiple transactions concurrently?
1. The lost update problem
2. The dirty read problem
3. The unrepeatable read problem
4. The phantom problem
Lost update problem, dirty read problem , unrepeatable read problem and phantom problems are the potential problem that might occur when a DBMS executes multiple transactions concurrently.
A trigger is
A trigger is actually a procedural code that is automatically executed in response to certain events on a particular table or view in a database.
Which of the following schemes are used for ensuring atomicity?
Following ensure atomicity:
• Log with deferred and immediate modification.
• Shadow paging.
Assume transaction A holds a shared lock R. If transaction B also requests for a shared lock on R, it will,
Since transaction A holds only a shared lock R.
Hence any number of transaction can read the data from the requested item using shared locking. Hence B’s request will be granted immediately Hence option (b) is correct.
Which of the following cannot be restarted?
Consider the following transaction schedule:
The labeled precedence graph will be
As we can see clearly T4 and T7 are followed by T3 and T4 in succeed by T3 and T7 and soon. Hence topological sequence represented by the above transactions is
Amongst the ACID properties of a transaction, the ‘Durability' property requires that the changes made to the database by a successful transaction persist
Consider the following three schedules of transactions T1, T2 and T3. [Notation: In the following NYO represents the action Y(Y for read, W for write) performed by transaction Non object O.]
Which of the following statements is TRUE?
As we can see S1 and S2 are conflict equivalent to each other. The equivalent serial schedule is
While the schedule S3 is having a conflicting pair hence equivalent serial schedule is not possible. Hence option (d) is correct.
In case Of timestamp ordering R-timestamp (Q) denotes