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Unformatted text preview: 8 OVERVIEW OF STORAGE AND INDEXING Exercise 8.1 Answer the following questions about data on external storage in a DBMS: 1. Why does a DBMS store data on external storage? 2. Why are I/O costs important in a DBMS? 3. What is a record id? Given a records id, how many I/Os are needed to fetch it into main memory? 4. What is the role of the buffer manager in a DBMS? What is the role of the disk space manager? How do these layers interact with the file and access methods layer? Answer 8.1 The answer to each question is given below. 1. A DBMS stores data on external storage because the quantity of data is vast, and must persist across program executions. 2. I/O costs are of primary important to a DBMS because these costs typically dominate the time it takes to run most database operations. Optimizing the amount of I/Os for an operation can result in a substantial increase in speed in the time it takes to run that operation. 3. A record id, or rid for short, is a unique identifier for a particular record in a set of records. An rid has the property that we can identify the disk address of the page containing the record by using the rid. The number of I/Os required to read a record, given a rid, is therefore 1 I/O....
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This note was uploaded on 01/17/2012 for the course EGN 4302 taught by Professor Dr.vishak during the Fall '12 term at University of Central Florida.
- Fall '12