Which of the following scenarios may lead to an irrecoverable error in a database system ?
(A) A transaction writes a data item after it is read by an uncommitted transaction
(B) A transaction reads a data item after it is read by an uncommitted transaction
(C) A transaction reads a data item after it is written by a committed transaction
(D) A transaction reads a data item after it is written by an uncommitted transaction
Answer: (D)
Explanation: Option C is a normal operation.
Option B is also fine as no write operation is involved.
Option A can be recovered, but option D can’t be.
See this for an example.
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