Though each database employs its own default level of locking for each operation, i is recommended for the applications to issue an explicit lock in the FOR UPDATE clause while retrieving data using SELECT statement. Hwever, isuing too frequent locks will slow down the performance of the application because when one user issues an explicit lock on a particular piece of data, te other users has to wait till the first user commits the changes to modify the same piece of data. Tis scenario is often called contention frequent contentions will impact the overall application to a worst extent.
Mintaining high level of data concurrency among multiple users without compromising the overall performance is a real challenge in the database design. Wen more than one user try to update the same piece of information, te changes or the updates made by one user will be partially or completely lost by the changes made by the other users. Tis scenario of data integrity issue is called ‘Lost updates’. Tis happens when users try to read uncommitted changes made users.
Fr example, tansaction A is modifying some piece of data and transaction B issues a query for the same data and reads few rows of uncommitted changes. Lter if transaction A rolls back the changes, ten the data read and processed by transaction B is not valid anymore and hence called ‘Dirty Read’. Tis scenario is met when the same query executed at a different point of time within the same application flow gives different result sets. Fr example, wen transaction A issues a query and reads piece data, bfore the end of this transaction another transaction B updates the same data, ten if transaction A issues the same query again, i would result in a different set of data.
Tis scenario is met when the same query executed at a different point of time within the same application flow gives unequal number of result sets. Fr example, wen transaction A issues a query and reads a piece of data, bfore the end of this transaction another transaction B inserts a new row, ten if A issues same query again, i would result in a new result set with different number of rows.
Ech database has a list of user names and its corresponding password. Acess to database is achieved only upon entering a valid user name and password. Aso, ech user in the list. ..
Please type your essay title, choose your document type, enter your email and we send you essay samples