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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
What is called mirroring? The simplest approach to introducing redundancy is to duplicate each disk. This method is called mirroring or shadowing.
Explain in details about the f unctions of DBA ?
What is the full form of DDL? DDL is stand for Data Definition Language.
Chapter 10a review questions
What function divides one numeric expression by another and returns the remainder? MOD function divides one numeric expression by another and returns the remainder.
What is normalization? It is a method of analysing the given relation schemas based on their Functional Dependencies (FDs) and primary key to attain the properties (1).Minim
to develop elrctronic database from manual forms
What is recursive closure? Why is it not possible to describe this operation in relational algebra? Recursive closure is applied to recursive relationship. An instance of rec
What is meant by heuristic optimisation?Discuss the major heuristics that are applied during query optimisation.
The Transactions- A transaction is definite as the unit of work in a database system. Database systems that deal with a huge number of transactions are also termed as transaction p
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