Lassonde School of Engineering Winter 2016 Term Course No: 4411 Database Management Systems

Transcription

1 Lassonde School of Engineering Winter 2016 Term Course No: 4411 Database Management Systems Last Name: First Name: Student ID: 1. Exam is 2 hours long 2. Closed books/notes

2 Problem 1 (6 points) Consider the following schema and query: Suppliers(sid, sname, city) Supply(did,pid) Parts(pid,pname,price) Select S.sname, P.pname From Suppliers S, Parts P, Supply Y Where S.sid=Y.sid and Y.pid=P.pid and S.city= Madison and P.price < List all left-deep plans for joins. 2. How would adding Distinct change a plan produced for this query.

3 3. Assume that the joins are executed as INL joins and that there is an index on P.price. Can you use that index in a query plan? If so, how; if not, why not?

4 Problem 2 (14 points): Short Answers 1. In the execution of a block nested loops join of R and S, is a record of R ever compared with a record of S and they do not match (on the join attribute(s))? If not, briefly explain how the block nested loops join method avoids this. If so, give an example of how this can occur. 2. In the execution of a hash join of R and S, is a record of R ever compared with a record of S and they do not match (on the join attribute(s))? If not, briefly explain how the hash join method avoids this. If so, give an example of how this can occur. 3. In the execution of a sort merge join of R and S, is a record of R ever compared with a record of S and they do not match (on the join attribute(s))? If not, briefly explain how the sort merge join method avoids this. If so, give an example of how this can occur.

5 4. Why are overflow chains in linear hashing of length one, on average? 5. In the hash join technique, why is a second hash function used to build the in-memory hash for each partition of the outer table? Why not just use the first hash function (which was used to create the partitions) again? 6. When a page in the buffer pool is modified, how does the DBMS ensure that this change is propagated to disk? 7. What happens if there is no page in the buffer pool with pin count = 0 and a page that is not in the buffer pool is requested?

6 Problem 3 (9 points): Consider table T with attributes A, B, C, D, & E. Table T has 1,000,000 records and T has no key. Column A has 10 values, Column B has 100 values, Column C has 1,000 values, , 000. Column D has 10,000 values, , 000. Column E has 100,000 values, , 000. Assume independence of the attributes, and a uniform distribution for each. The following are possible indexes for T. 1 B+ tree unclustered index on D + C + B. 2 B+ tree clustered index on D + B + C. 3 B+ tree clustered index on C + A + B + D. 4 hash unclustered index on A + B + D + E. 5 hash clustered index on A + B + E. 6 hash clustered index on D + A + B + E. Assume that the depth of each B+ tree above is four: so it costs four I/O s from the root to the data entry page. Assume the hash indexes are extendible hashes, so one I/O to get the directory page and one I/O to get the data entry page (or the data record page itself, if clustered), so two I/O s. We are interested to retrieve records from T that satisfy where A = 7 and B = 53 and D < 1,001 and E > 40,000 and E < 41, (2 points) Estimate how many records will be retrieved.

7 2. (4 points) Which index provides the best access path? What is its I/O cost? 3. (3 points) Assuming that many tuples are returned, which index provides the best access path and preserves an interesting order on D? What is its I/O cost?

8 Problem 4 (11 points): Indicate whether each of the following statements is TRUE or FALSE. You will get 1 point for each correct answer and 0.5 point for each incorrect answer. 1. The LRU algorithm should not be used for the buffer management of B+-tree indexes. 2. Consider relations R(A, B) and S(B, C) where N R = 2000, N S = 1000, and B is a key for S. The expected number of tuples in R S is less than or equal to The merge join algorithm should be used for a natural join operation only when the joined relations are sorted, because in cases where the joined relations are not sorted the hash join algorithm is faster. 4. It is always better to store a sorted file in as few blocks as possible, because that can reduce the disk I/O s when the file is accessed. 5. Any relational algebra expression consisting of select (δ), project (π), and join ( ) operators can be transformed to the form π A (δ C (R 1 R n )), where A is an attribute list, C is a selection condition, is the cross-product operator, and R i are the operand relations. 6. Assume the following are all discovered frequent (that is, are above the minimum support) itemsets: {1,2,3}, {1,2,4}, {1,3,4}, {1,3,4}. No 4-itemsets can possibly be frequent. 7. Extendible hash index does not use overflow buckets. 8. A bitmax index is useful only for sparse attributes. 9. Semantic query optimization uses information about triggers to optimize queries. 10. The Bloomjoin technique is designed to save I/O. 11. Dynamic query optimization is a response to inaccurate estimates of cardinalities of query operators.