Sometimes a transaction has to be undone after it has committed because it was erroneously executed—for example, because of erroneous input by a bank teller. a. Give an example to show that using the normal transaction undo mechanism to undo such a transaction could lead to an inconsistent state. b. One way to handle this situation is to bring the whole database to a state prior to the commit of the erroneous transaction (called point-in-time recovery). Transactions that committed later have their effects rolled back with this scheme. Suggest a modification to the recovery algorithm of Section 19.4 to implement point-in-time recovery using database dumps. c. Later nonerroneous transactions can be reexecuted logically, if the updates are available in the form of SQL but cannot be reexecuted using their log records. Why?
Sometimes a transaction has to be undone after it has committed because it
was erroneously executed—for example, because of erroneous input by a bank
teller.
a. Give an example to show that using the normal transaction undo
b. One way to handle this situation is to bring the whole
prior to the commit of the erroneous transaction (called point-in-time recovery). Transactions that committed later have their effects rolled back
with this scheme.
Suggest a modification to the recovery
implement point-in-time recovery using database dumps.
c. Later nonerroneous transactions can be reexecuted logically, if the updates are available in the form of SQL but cannot be reexecuted using
their log records. Why?
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