COMP 266 Lecture 6: Questio6

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Question: Consider the concurrent execution
of the following...
Consider the concurrent execution of the following transactions.
T1 T2
Read A Read B
Read B Write A
Write C Read C
Write A Write B
Commit Commit
List two problems that may occur from the concurrent execution of these two transactions.
Expert Answer
If there are two transactions we have then there will be differnt problems may arise...
1-Incorrect Summary problem
2-Lost Update problem
3-Dirty Read Problem
T1 T2
Read A Read B
Read B Write C
Write C Read C
Write A Write B
Commit Commit
Case 1
Transaction T1 is reading A and T2 is reading B which is perfectlying fine because bothe
are performing action on A and B which is difffrent.
Case 2
Transaction T1 is reading B and T2 is writing A which will create no problem because T1
is tring to read B which is free because at that time T2 is writng on A and T1 is not doing
anthing on A.
Case 3
It will definately create a problem because because T1 is writing on C at the same time
T2 is reading it.So it may be a problem of dirty read because T2 is not updatede yet about
the writing of T1 on C
Case 4
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