ΗΥ460 Συστήματα Διαχείρισης Βάσεων Δεδομένων Χειμερινό Εξάμηνο 2017 Διδάσκοντες: Βασίλης Χριστοφίδης, Δημήτρης Πλεξουσάκης, Χαρίδημος Κονδυλάκης

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1 ΗΥ460 Συστήματα Διαχείρισης Βάσεων Δεδομένων Χειμερινό Εξάμηνο 2017 Διδάσκοντες: Βασίλης Χριστοφίδης, Δημήτρης Πλεξουσάκης, Χαρίδημος Κονδυλάκης Exercise 1 (15 points) Disk Storage Λύσεις 1 ης σειράς Ασκήσεων Ημερομηνία Παράδοσης: 20/10/2017 When indicated or needed please assume a storage system with the following parameters: B block size 2400 bytes Bfr no. of records per block 6 btt block transfer time 0.8 ms (data transfer rate is 3000 bytes/ms) ebt effective block transfer time 0.84 ms (effective data transfer rate is 2857 bytes/ms) r average rotational latency time 8.3 ms s average seek time 16 ms Consider a sorted sequential file with an overflow area in an IBM 3380 disk environment. The file contains 300,000 records in the sorted part and 100,000 records in the overflow part (Take record size as 400 bytes). a. (10pts.) Find the time needed for a successful search. b. (5pts) Find the time needed for an unsuccessful search. Exercise 2 (10 points) Storage We are using the indirection-in-block approach (shown in Figure) for storing records in each block. We have 8192-byte blocks in which we store fixed-length records of 39 bytes. The block header consists of a 4-byte pointer to the next block plus an offset table that consists of 2-byte pointers to records within the block. On an average day, 8 records per block are inserted, and 5 records are deleted. A deleted record must have its pointer replaced by a tombstone, because there may be dangling pointers to it. For specificity, assume the deletions on any day always occur before the insertions. If the block initially (that is, at the beginning of day 1, before any operations performed) contains 10 records, for how many days will there be enough room to insert more records? (It might be the case that on the last day less than 8 records are inserted. If the last insertion of a record occurs on day 1, the answer is 1 days; if it occurs on day 2, the answer is 2 days; and so on.)

2 Figure: Indirection in block Exercise 3 (25 points) Extendible hashing In an extendible hashing environment the directory level directory depth- (d) is given as 10. In this environment the size of each directory row is given as 4 bytes. Assume that the data bucket size is 2400 bytes and the record size is 400 bytes. Answer the following questions. a) (2pts.) In an environment like this how many directory entries would you have (i.e., specify the number of rows in the index table)? b) (2pts.) If each directory entry requires 4 bytes what is the total size of the directory? c) (3pts.) What can be the maximum file size in terms of number of records? d) (3pts.) In a file like this what is the minimum number of buckets with bucket depth (p) of 9? e) (5pts.) In a file like this what is the maximum number of buckets with bucket depth (p) of 9? f) (3pts.) In a file like this what is the minimum number of buckets with bucket depth (p) of 10? g) (2pts.) In a file like this what is the maximum number of buckets with bucket depth (p) of 10? h) (5pts.) In an environment like this what is the minimum and maximum I/O time to read 10 records. Assume that we keep the directory in main memory.

3 Άσκηση 4 (25 points) Linear Hashing In a linear hashing environment we have 30 primary area buckets. Bucket size is 2400 bytes and record size is 400 bytes, LF (load factor) of the file is 0.67 (or 67%). a) (6pts.) What is the hashing level h? b) (2pts.) What is the boundary value (bv)? c) (6pts.) How many primary area buckets are hashed at level h? d) (2pts.) How many primary area buckets are hashed at level (h+1)? e) (3pts.) How many records do we have in the file? f) (3pts.) After inserting how many records does the value of bv (boundary value) change? g) (3pts.) In this configuration what is the minimum I/O time to access a record? Exercise 5 (25 points) Physical Design Consider the relations: Student(id#, name, age, course) Subject(code, title, description) which contain 50,000 and 5,000 records respectively and are stored in files sorted on id# and code respectively. Imagine that we are using simple flat indexes (because e.g. the files are reasonably static). a) (1 pt) On which fields could you build a dense index? b) (2 pts) On which fields could you build a non-dense index? c) (3 pts) If the student id# is a 4-byte quantity, block-address are 4-bytes long, and pages are 4KB, how large would dense indexes on Student.id# and Subject.code be? d) (3 pts) If the Nr(Student) = 100 and Nr(Subject) = 20, and other values are as above, how large would non-dense indexes on Student.id# and Subject.code be? e) If you had just dense indexes on Student.id# and Subject.code, briefly describe efficient processing strategies for the following queries: (2 pts) select name from Student where id= (2 pts) select title from Subject where code >= 'COMP1000' and code <= 'COMP2000'

4 (2 pts) select id#,name from Student where age=18 (2 pts) select code,title from Subject where title like '%Comput%' (8 pts) What techniques could you use to improve the performance of each of the above queries? And how would it impact the other queries? Exercise 6 (10 points) Buffer Management In this exercise, you will compare the LRU, MRU, and CLOCK buffer management algorithms for a given workload (just as you did in the first part of homework 1). Here are the assumptions you must make: Assume there are four page slots your buffer manager must manage: P1, P2, P3, and P4. All four slots are empty to start. When the buffer pool has unused slots (such as at the beginning, when all four slots are empty), it will put newly read data in the leftmost empty slot (e.g., if slots 2 and 3 are free, it will use slot 2). The pages to be read from disk are labelled A through G. For each access the page is pinned, and then immediately unpinned. Below are three tables for describing the contents of the buffer pool at each time step. A page is read at the beginning of each time step. You should record, in the table, the contents of each Buffer Page after the new page has been read in. Time Page Read 1 G 2 F 3 E 4 D 5 G 6 C 7 F 8 E 9 D LRU (3 points) Buffer page P1 P2 P3 P4

5 10 C 11 D 12 B 13 A 14 D 15 F Total number of pages evicted : Time Page Read 1 G 2 F 3 E 4 D 5 G 6 C 7 F 8 E 9 D 10 C 11 D 12 B 13 A 14 D 15 F LRU (3 points) Buffer page P1 P2 P3 P4 Total number of pages evicted :

6 Time Page Read 1 G 2 F 3 E 4 D 5 G 6 C 7 F 8 E 9 D 10 C 11 D 12 B 13 A 14 D 15 F CLOCK (4 points) Buffer page P1 P2 P3 P4 Total number of pages evicted :

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IMPORTANT: Circle the last two letters of your class account: Spring 2011 University of California, Berkeley College of Engineering Computer Science Division EECS MIDTERM I CS 186 Introduction to Database Systems Prof. Michael J. Franklin NAME: STUDENT ID: IMPORTANT: