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Hashing


1. 6.6Assume a relation with key attribute of type integer, and give examples of the following. (R11)


a. A linear hashing index and an extensible hashing index with the same data entries, such that the linear hashing index has more pages.


b. A linear hashing index and an extensible hashing index with the same data entries, such that the extensible hashing index has more pages.


Do my coursework


Specify what hashing function you have chosen. Draw appropriate diagrams. Remember to include the additional directory page for the extensible hashing index in the page count.


. Consider the ¡°llps¡± graph in slide 155 of the lecture notes.


a. What is a probe sequence? Where does it start and where does it end?


b. Given your definition of a probe sequence, assume a uniform hash function h, and assume just one record per bucket. Thinking about the situation where the llps graph was obtained, is it possible to experimentally reproduce that type of graph for


¡ì simple unindexed hash tables of fixed size T ?


¡ì linear hashing indexes?


¡ì extensible hashing indexes?


Use one of the words ¡°always-never-sometimes¡± to respond, and briefly justify each answer.


Index Construction and Sorting


. Consider ¡°replacement sort¡± as described in slides 188-18 and in section 1..1 of the textbook.


a. Assuming all tuples to be of the same size, write pseudocode for the replacement sort. Note You may use more than one pseudocode module.


b. What portions of your pseudocode would change for handling tuples of unequal size? Do not write the pseudocode, just provide a reasonable strategy. (R1)


Pipelining in Query Processing


4. Refer to the ¡°Research¡± sample database, accessible in read-only mode in yallara, through the sqlresearch command in Unix (no Oracle account is needed).


a. Create an example of an SQL query against this database, where a subquery includes a join whose result needs materialisation, that is, the query cannot be pipelined.


b. Assume you are working for a large corporation managing a set of good sized tables, even larger than the ones in the Research database. Can every query that has joins, but no subquery, be pipelined? Explain. (R1)


Query Optimisation


5. Consider the relations R1(A, B, C), R(C, D, E) and R(E, F), with primary keys A, C and E respectively. Assume that R1 has 000 tuples, R has 000 tuples, and R has 100 tuples. (S14)


a. Estimate the maximum possible size of the join of the three relations, R1 wv R wv R.


b. Propose an efficient strategy for computing the join. Assume indexes can be created and the cost of creating indexes is insignificant.


Transactions


6. Consider the following classes of schedules serializable, conflict-serializable, recoverable, avoids-cascading-aborts, and strict. For each of the following schedules, indicate and justify which of the preceding classes it belongs to. If you cannot decide whether a schedule belongs in a certain class based on the listed actions, explain briefly. (R17)


a. r1(X), w(X), w1(X), a, c1


b. w1(X), r(X), w1(X), a, c1





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