Explain the term memory hierarchy. What are the differences between primary, secondary, and tertiary storage? Give examples of each. Which of these isvolatile, and which are persistent? Why is persistent storage more important for a DBMS than, say, a program that generates prime numbers? (Section 9.1)
Why are disks used so widely in a DBMS? What are their advantages over main memory and tapes? What are their relative disadvantages? (Section 9.1.1)
What is a disk block or page? How are blocks arranged in a disk? How does this affect the time to access a block? Discuss seek time, rotational delay, andtransfer time. (Section 9.1.1)
Explain how careful placement of pages on the disk to exploit the geometry of a disk can minimize the seek time and rotational delay when pages are read sequentially. (Section 9.1.2)
Explain what a RAID system is and how it improves performance and reliability. Discuss striping and its impact on performance and redundancy and its impact on reliability. What are the trade-offs between reliability Page 334and performance in the different RAID organizations called RAID levels?(Section 9.2)
What is the role of the DBMS disk space manager? Why do database systems not rely on the operating system instead? (Section 9.3)
Why does every page request in a DBMS go through the buffer manager? What is the buffer pool? What is the difference between a frame in a buffer pool, a page in a file, and a block on a disk? (Section 9.4)
What information does the buffer manager maintain for each page in the buffer pool? What information is maintained for each frame? What is the significance of pin_count and the dirty flag for a page? Under what conditions can a page in the pool be replaced? Under what conditions must a replaced page be written back to disk? (Section 9.4)
Why does the buffer manager have to replace pages in the buffer pool? How is a page chosen for replacement? What is sequential flooding, and what replacement policy causes it? (Section 9.4.1)
A DBMS buffer manager can often predict the access pattern for disk pages. How does it utilize this ability to minimize I/O costs? Discuss prefetching. What is forcing, and why is it required to support the write-ahead log protocol in a DBMS? In light of these points, explain why database systems reimplement many services provided by operating systems. (Section 9.4.2)