14,690 views
51 votes
51 votes

Which of the following scenarios may lead to an irrecoverable error in a database system?

  1. A transaction writes a data item after it is read by an uncommitted transaction
  2. A transaction reads a data item after it is read by an uncommitted transaction
  3. A transaction reads a data item after it is written by a committed transaction
  4. A transaction reads a data item after it is written by an uncommitted transaction

5 Answers

Best answer
47 votes
47 votes
  1. Here if transaction writing data commits , then transaction which read the data might get phantom tuple/ Unrepeatable error. Though there is no irrecoverable error possible even in this option.
  2. This is non issue. Both transaction reading data.
  3. This is non issue.
  4. This is dirty read. In case if transaction reading uncommitted data commits, irrecoverable error occurs of uncommitted transaction fails. So (D) is answer
edited by
8 votes
8 votes

 

I hope now it is clear which is the only case where IRRECOVERABILITY ARISES.

That is only when a particular transaction reads from a uncommited Transacation and , commits before the commit of the transaction whose data it was reading.

edited by
7 votes
7 votes
D. If Data is uncommitted , then transactions reads a data after write always give error.
3 votes
3 votes
D

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.
Answer:

Related questions

25 votes
25 votes
3 answers
2
Kathleen asked Sep 16, 2014
23,359 views
Suppose the numbers $7, 5, 1, 8, 3, 6, 0, 9, 4, 2$ are inserted in that order into an initially empty binary search tree. The binary search tree uses the usual ordering o...
55 votes
55 votes
6 answers
3
44 votes
44 votes
5 answers
4