Question
Consider the following schedule involving two transactions T1 and T2 operating on a dataset
table storing aggregate metrics:
| Time | T1 | T2 |
|---|---|---|
| t1 | READ(X) | |
| t2 | X = X + 50 | |
| t3 | READ(X) | |
| t4 | X = X * 1.2 | |
| t5 | WRITE(X) | |
| t6 | WRITE(X) |
i. Compute the final value of X (assume initial X = 100).
11. Determine whether the schedule is serializable.
iii. Identify the concurrency issue involved and explain its impact on analytics accuracy.
Answer :
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Skip in 10
Transaction T1 first reads X with an initial value of 100 and then computes a new value by adding 50, giving a local value of 150. However, this value is not written immediately to the database. Before T1 writes back, transaction T2 reads X from the database, still obtaining the old value of 100 because T1’s update is not yet stored. T2 then multiplies this value by 1.2, producing 120, and writes 120 to the database.
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