A common rule to follow when blogging is _____.
A. copy content from Web sites to use on your blog
B. never give credit to those posting on your blog
C. proofread and check your grammar and spelling
D. never respond to those posting comments
Answer: C
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Assume that each individual SQL statement is executed in isolation, that the DBMS uses intention locking and sets locks on tables and rows, and that host variable f contains the number of the flight to be booked. The transaction should not overbook the flight.
An airlines database has two tables: Flights, with attributes flt_num, plane_id, num_reserv; and Planes, with attributes plane_id, and num_seats. The attributes have the obvious semantics. A reservation transaction contains the following steps:
SELECT F.plane_id, F.num_reserv INTO :p, :n FROM Flights F WHERE F.flt_num = :f A. SELECT P.num_seats INTO :s FROM Planes P WHERE P.plane_id = :p B. . . . check that n < s ... C. UPDATE Flights F SET F.num_reserv = :n + 1 WHERE F.flt_num = :f D. COMMITa. Assuming that the transaction is run at READ COMMITTED, w hat locks are held at points A, B, and D? b. The database can be left in an incorrect state if concurrently executing reservation transactions that are running at READ COMMITTED are interleaved in such a way that one transaction is completely executed at point B in the execution of another. Describe the problem. c. In an attempt to avoid the problem described in (b), the SET clause of the UPDATE statement is changed to F.num_reserv = F.num_reserv + 1. Can reservation transactions nowbe run correctly at READ COMMITTED? Explain. d. Assuming that the transaction is run at REPEATABLE READ and that the tables are accessed through indices, what table locks are held at points A, B, and D? e. What problem does the interleaving of (b) cause at REPEATABLE READ? Explain. f. Does the interleaving of (b) cause an incorrect state if the transaction (either version) is run using SNAPSHOT isolation? Explain. g. To keep track of each passenger, a newtable, Passenger, is introduced that has a rowdescribing each passenger on each flight with attributes name, flt_num, seat_id. SQL statements are appended to the end of the transaction (1) to read the seat_id’s assigned to each passenger on the flight specified in f and (2) to insert a rowfor the newpassenger that assigns an empty seat to that passenger. What is the weakest ANSI isolation level at which the transaction can be run without producing an incorrect state (i.e., two passengers in the same seat)? Explain.
MP3 players are ideal for high-impact activities because they do not contain any moving parts
Indicate whether the statement is true or false
? A background image can be placed using the keywords left, center, and right for the vertical position and top, center, and bottom for the horizontal position.
Answer the following statement true (T) or false (F)
Which of the following is a firewall best able to control?
What will be an ideal response?