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Wait-die" scheme: The idea is based on non-preventive method. It is based on a simple rule:
If Ti requests a database resource that is held by Tj
then if Ti has a smaller timestamp than that of Tj
it is permitted to wait;
else Ti aborts.
A timestamp may loosely be described as the system generated sequence number that is unique for every transaction. Therefore, a smaller timestamp means an older transaction. For example, suppose that 3 transactions T1, T2 and T3 were generated in that series, then if T1requests for a data item which is presently held by transaction T2, it is permitted to wait as it has a smaller time stamping than that of T1. Though, if T3 requests for a data item which is presently held by transaction T2, then T3 is rolled back (die).
Figure: Wait-die Scheme of Deadlock prevention
If R1 and R2 are two relations or functions, then the result of R3 = R1 × R2 is the combination of tuples that are in R1 and R2. The product is associative and commutative. Degr
.#question. Discuss the problem which may arise during concurrency control and recovery in distributed database which are not encountered in controlized database environment.
List the requirements needed to design a trigger. The requirements are:- Specifying when a trigger is to be implemented. State the actions to be taken when the trigger im
complete er diagram of textile industry management
Accessing information about permissions to all users- Object level permissions: With the use of data dictionary you can see the permissions to user. Let us get the table name fro
A distributed database is defined as "a collection of multiple logically interrelated database which are physically distributed over a computer network" (a) Give any three advan
What is NULL? Simply NULL means not in value.
What are audit trails? An audit trail is a log of all alters to the database along with information like which user performed the change and when the alter was performed.
how map binary relation one to one
We face problem of stock Opening balance and closing balance in Minus
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