Premium Essay

Dbms Function

In: Computers and Technology

Submitted By Browneyez66
Words 965
Pages 4
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 8:10.
In transaction 2, the DBMS started it at 8:01, added an Orders table record at 8:02, and added an Order Line table record at8:05 and added an Order Line table record at 8:09. To roll back 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. (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. An unrepeatable read (also called an inconsistent retrieval, dirty read, or inconsistent read) occurs when a user’s retrieval transaction reads a set of data that other users’ transactions have partially updated. For example, suppose Pat’s transaction involves calculating the total balance for all customers, and the customer balances are $900, $750, and $500for a total of $2,150. Suppose further that a $200 order from the third customer was entered for the first customer by mistake, and that Elena’s update transaction will change the customer for that order from the first

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