One morning the chief information officer (CIO) called an emergency meeting of t

Question

One morning the chief information officer (CIO) called an emergency meeting of the system administration team. As a database administrator, you are part of this team. The meeting was about a data inconsistency problem in a newly launched web application. The database in question deals with items and their prices. Your colleague in charge of the problematic database noticed that the phantom problem is happening while the application is following the strict 2PL protocol. He explained that while a first transaction (T1) has locked all existing items of type 1, a second transaction (T2) was able to add new items of type 1 at the same time, which caused the average price calculated by T1 to be incorrect when displayed to the user. The CIO asked the rest of you to check whether the same problem is happening in the databases you are in charge of. Can this Phantom problem occur in any of your databases where the set of database objects is fixed and only the values of objects can be changed? Explain.

Explanation / Answer

The Phantom problem occurs when a transcation retrieves a collection of objects and produces different values when accessing same data for diffrent times,even though it has not modified and has locked using Strict 2PL protocal.This phantom problem generally occurs in dynamic databases where a transaction is supposed to be locked all objects of given type.

Like the specified problem when a transaction T1 locked all existing items of type 1.the second transaction T2 can add the items to type 1 which leads to the inconsustency.where T1 cannot assume it has locked all items in that type 1.

Comming the other databases where the set of database objects is fixed and only the values of objects can be changed,on this databases the phontom problem cannot occur because one cannot insert new objects into the database if the set of DB objects is fixed.

Any transaction access the database and retrive the information by objects the insertion,deletion operations are performed on this objects only.Where if these objects are fixed we can't add or delete these objects,these objects contains reference data include tables, views, clusters, sequences, indexes, and synonyms.Tables are primary storage of data.when they are fixed then multiple transactions on same data cant be performed so phantom problem cant occur in databases with fixed objects.

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