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 record’s id, how many I/Os are needed to fetch it into main memory?
4. What is the role of the bu?er manager in a DBMS? What is the role of the disk space manager? How do these layers interact with the ?le and access methods layer?
2.Consider a relation stored as a randomly ordered ?le for which the only index is an unclustered index on a ?eld called sal. If you want to retrieve all records with sal > 20, is using the index always the best alternative? Explain.