Describe the four levels of isolation in SQL. Define the violations caused by each of the following: dirty read, nonrepeatable read, and phantoms. Change transaction Tz in Figure 17.2b to read...

Describe the four levels of isolation in SQL.

Define the violations caused by each of the following: dirty read, nonrepeatable

read, and phantoms.

Change transaction Tz in Figure 17.2b to read

read_; tem(X) ;

X:= X+M;

if X > 90 then exit

else wr;te_;tem(X);

Discuss the final result of the different schedules in Figure 17.3(a) and (b), where

M = 2 and N = 2, with respect to the following questions. Does adding the above

condition change the final outcome? Does the outcome obey the implied consistency rule (that the capacity of X is 90)?