Total = 16/20 points
For the following exercises, you will address problems and answer questions from management at Premiere Products. You do not use the Premiere Products database for any of these exercises.
1 . While users were updating the Premiere Products database, one of the transactions was interrupted. You need to explain to management what steps the DBMS will take to correct the database. Using the sample log in Figure 7-1 1 , list and describe the updates that the DBMS will roll back if transaction 2 is interrupted at 8:1 0.
In transaction 2, the DBMS started it at 8:01, added an Orders table record at 8:02, added an OrderLine table record at 8:05, and added an OrderLine table record at 8:09. To rollback the transaction, the DBMS deletes the three added records.
2. Occasionally, users at Premiere Products obtain incorrect results when they run queries that include built-in (aggregate, summary , or statistical) functions. The DBA told management that unrepeatable reads caused the problems. Use books, articles, and/or the Internet to research the unrepeatable read problem. Write a short report that explains the unrepeatable-read problem to management and use an example with y our explanation.
(Note: Unrepeatable reads are also called inconsistent retrievals, dirty reads, and inconsistent reads.)
Unrepeatable-Read Problems occur many times when a different result is seen from the same query while still in progress. This usually happens when dealing with the UPDATE command by other transactions.