Using the result of Exercise 11.13, showwhich of the enhanced plans can be further enhanced by adding the duplicate elimination operator ? introduced in Exercise 11.9.
What will be an ideal response?
Since projections applied to Professor must always preserve the attribute Id for the subsequent join and since this attribute forms a key, no duplicates are possible and, thus, ? would be useless after such a projection (and might actually incur costs only to ?nd out that the operation has no e?ect).
In case of Teaching, as discussed in the solution to exercise 11.13, projection (?ProfId) can be pushed only in cases (b) and (d), because in other cases we use the index on the attribute ProfId. Since in a given semester a professor teaches on the average of two courses, duplicate elimination would reduce the size of the intermediate relation by the factor of two, maybe three. Let us examine whether the cost of such duplicate elimination is justi?ed by the savings in computing the subsequent join.
In case (d), since sort-merge-join is used, the operands must be sorted anyway, so duplicate elimination can be done at no cost and would reduce the overall cost of the join.
In case (b), the result of selection on Teaching has 250 pages. Since in this example we use a 51-page bu?er, 5 runs can be produced at the cost of 500 I/Os (read then write), and then they are merged and duplicates eliminated at the cost of
another 250 I/Os (to just read the runs into the main memory). Thus, using duplicate elimination does not make sense in this case, because the total estimated cost of plan (b) in Figure 11.3 was just 512 pages.
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Match each term with the correct statement below.
A. A formal statement of best practices promulgated by an agency with the formal authority to issue them B. Allow managers to chart the organization's course over time C. Requirements dictated by an agency or other legally constituted unit, which must be complied with D. A process of gathering evidence and drawing conclusions about the correctness or quality of a given subject E. Designates a condition or state in which the organization can be assured to satisfy relevant legal and regulatory requirements F. The process of generating proof and drawing conclusions from the evidence that can be attested to G. Legal mandates dictated by a body with the authority to issue those mandates H. Documents how the organization will verify and validate that the execution of the compliance function is correct I. The specific activities that will be undertaken to satisfy some policy dictate
The command "ipconfig /renew" can be used to renew the IPv6 address for the specified adapter.
Answer the following statement true (T) or false (F)
The sequence in which the pages are printed.
What will be an ideal response?
?What two ps options can be used to display a full list of information about each process, and a long list of information about each process?
A. ?-e B. ?-p C. ?-f D. ?-l