Give an example of a schedule executing at SNAPSHOT isolation in which two transactions each introduce a phantom that is not seen by the other transaction, resulting in incorrect behavior. Assume that the data items referred to in the description of SNAPSHOT isolation are rows.

What will be an ideal response?

p is a predicate over a particular table and x and y are rows satisfying p.
SELECT1(p) SELECT2(p) INSERT1(x) INSERT2(y)
An integrity constraint states that there can be no more than n items in the database
satisfying predicate p. Each transaction reads the tuples satisfying p finds there are
exactly (n ? 1) and therefore inserts a newtuple satisfying p. At the end there are
(n + 1) tuples satisfying p