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Classify concurrency anomaly between two transactions

BitkernelSoftware Engineer · Online Assessment
MediumSoftware EngineerOnline AssessmentSoftware Engineering Fundamentals

Last updated

This question evaluates proficiency in database concurrency control and transaction isolation within the Software Engineering Fundamentals domain, focusing on identifying concurrency anomalies that affect data integrity and update correctness.

Two transactions T1 and T2 run concurrently and access the same data item A. Their operations (in order of time) are:

  1. T1 reads A = 100.
  2. T2 reads A = 100.
  3. T1 writes A = A + 10 (so conceptually writes 110).
  4. T2 writes A = A - 10 (using its previously read value 100, so writes 90).

Which description best characterizes the concurrency problem here?

Options:

  • A. This operation cannot be repeatably read (non-repeatable read).
  • B. This operation has no problems.
  • C. This operation reads dirty data.
  • D. This operation loses modifications (lost update).