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Exercise 9.15 Modern disks often have their own main memory caches, typically about 1 MB, and use this to prefetch pages. The rationale for this technique is the em- pirical observation that, if a disk page is requested by some (not necessarily database!) application, 80% of the time the next page is requested as well. So the disk gambles by reading ahead. 1. Give a nontechnical reason that a DBMS may not want to rely on prefetching controlled by the disk. 2. Explain the impact on the disk's cache of several queries running concurrently, each scanning a different file. 3. Is this problem addressed by the DBMS buffer manager prefetching pages? Ex- plain. 4. Modern disks support segmented caches, with about four to six segments, each of which is used to cache pages from a different file. Does this technique help, with respect to the preceding problem? Given this technique, does it matter whether the DBMS buffer manager also does prefetching?

Exercise 9.15 Modern disks often have their own main memory caches, typically about 1 MB, and use this to prefetch pages. The rationale for this technique is the em- pirical observation that, if a disk page is requested by some (not necessarily database!) application, 80% of the time the next page is requested as well. So the disk gambles by reading ahead. 1. Give a nontechnical reason that a DBMS may not want to rely on prefetching controlled by the disk. 2. Explain the impact on the disk's cache of several queries running concurrently, each scanning a different file. 3. Is this problem addressed by the DBMS buffer manager prefetching pages? Ex- plain. 4. Modern disks support segmented caches, with about four to six segments, each of which is used to cache pages from a different file. Does this technique help, with respect to the preceding problem? Given this technique, does it matter whether the DBMS buffer manager also does prefetching?

Computer Networking: A Top-Down Approach (7th Edition)
Computer Networking: A Top-Down Approach (7th Edition)
7th Edition
ISBN:9780133594140
Author:James Kurose, Keith Ross
Publisher:James Kurose, Keith Ross
Chapter1: Computer Networks And The Internet
Section: Chapter Questions
Problem R1RQ: What is the difference between a host and an end system? List several different types of end...
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Exercise 9.15 Modern disks often have their own main memory caches, typically about 1 MB, and use this to prefetch pages. The rationale for this technique is the em- pirical observation that, if a disk page is requested by some (not necessarily database!) application, 80% of the time the next page is requested as well. So the disk gambles by reading ahead. 1. Give a nontechnical reason that a DBMS may not want to rely on prefetching controlled by the disk. 2. Explain the impact on the disk's cache of several queries running concurrently, each scanning a different file. 3. Is this problem addressed by the DBMS buffer manager prefetching pages? Ex- plain. 4. Modern disks support segmented caches, with about four to six segments, each of which is used to cache pages from a different file. Does this technique help, with respect to the preceding problem? Given this technique, does it matter whether the DBMS buffer manager also does prefetching?
Transcribed Image Text:Exercise 9.15 Modern disks often have their own main memory caches, typically about 1 MB, and use this to prefetch pages. The rationale for this technique is the em- pirical observation that, if a disk page is requested by some (not necessarily database!) application, 80% of the time the next page is requested as well. So the disk gambles by reading ahead. 1. Give a nontechnical reason that a DBMS may not want to rely on prefetching controlled by the disk. 2. Explain the impact on the disk's cache of several queries running concurrently, each scanning a different file. 3. Is this problem addressed by the DBMS buffer manager prefetching pages? Ex- plain. 4. Modern disks support segmented caches, with about four to six segments, each of which is used to cache pages from a different file. Does this technique help, with respect to the preceding problem? Given this technique, does it matter whether the DBMS buffer manager also does prefetching?
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