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Explain Two phase locking protocol
A transaction is consider as to follow the two-phase locking protocol if all locking operations precede the first unlock operation in the transaction. Such type of transaction can be divided into two phases: and expanding or growing (first) phase, throughout which new locks on items can be acquired but none can be released; and a shrinking (second) phase, throughout which existing locks can be released but no new locks can be obtained. This two-phase protocol can make sure the serializability because all the data items needed by a transaction will be locked at the starting of the transaction and if other transaction needs to use those data items then it has to wait till they become unlocked.
What is trigger? Triggers are statements that are executed automatically by the system as the side effect of a modification to the database.
Consider the following database schema: STAFF(StaffNo, fName, lName, Position, sex, dob, branchNo) BRANCH(BranchNo, Street, City) Assume the following for the above database
why are older data models are being replaced by new data models
Write short notes on transaction state? A transaction may not always complete its implementation successfully such a transaction is termed aborted A transaction must be in o
Adding Redundant Associations for Efficient Access The expression redundant association means using "duplicate association for proficient access". While analysis, it is not a
What is a SELECT operation? The select operation selects tuples that please a given predicate. We use the lowercase letter σ to denote selection.
Lost Updates : Suppose the two transactions T3 and T4 run simultaneously and they happen to be interleaved in the following way (suppose the initial value of X as 10000):
i need help with creating database system for a library
Define the following constraints for the table client. (i) BAL_DUE must be at least 1000. (ii) NAME is a unique key. (i)ALTER TABLE CLIENT ADD CONSTRAINT CLIENT_BAL_DUE_C1
Why a report generator is used ? Report generator is used for print files on paper.
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