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Lanchester Liners Hospitality Database

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Though each database employs its own default level of locking for each operation, it is recommended for the applications to issue an explicit lock in the FOR UPDATE clause while retrieving data using SELECT statement. However, issuing 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, the other users has to wait till the first user commits the changes to modify the same piece of data. This scenario is often called contention and too frequent contentions will impact the overall application to a worst extent. Maintaining high level of data concurrency among multiple users without compromising the overall performance is a real challenge in the database design.When more than one user try to update the same piece of information, the changes or the updates made by one user will be partially or completely lost by the changes made by the other users. This scenario of data integrity issue is called ‘Lost updates’.This happens when users try to read uncommitted changes made by other users. For example, transaction A is modifying some piece of data and transaction B issues a query for the same data and reads few rows of uncommitted changes. Later if transaction A rolls back the changes, then the data read and processed by transaction B is not valid anymore and hence called ‘Dirty Read’.This scenario is met when the same query executed at a different point of time within the same application flow gives different result sets. For example, when transaction A issues a query and reads a piece of data, before the end of this transaction another transaction B updates the same data, then if transaction A issues the same query again, it would result in a different set of data.This 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. For example, when transaction A issues a query and reads a piece of data, before the end of this transaction another transaction B inserts a new row, then if transaction A issues the same query again, it would result in a new result set with different number of rows.Each database has a list of user names and its corresponding password. Access to database is achieved only upon entering a valid user name and password. Also, each user in the list
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