ITPEC IP April 2021 Question 26
In DBMS, which of the following is a function for maintaining consistency of data by preventing the occurrence of conflicts due to simultaneous access to the data?
Explanation
Exclusive control — the DBMS locks data so that simultaneous updates cannot conflict.
If two transactions both read a stock of 10 and each subtracts 1, both write back 9 and one update is lost. With exclusive control the first transaction locks the record; the second waits until the lock is released and then reads the updated 9, so the result is 8 and the data stays consistent. A shared lock lets several readers in together; an exclusive lock admits one writer only.
Answer (c)
Why not others:
- •(a) Normalization — splits tables to remove redundancy and update anomalies; it is a design step, not control of simultaneous access
- •(b) Deadlock — not a function but a problem that locking can cause: two transactions each waiting for the other's lock
- •(d) Restore — recovers data from a backup after a failure
Key rule: Concurrent access is kept consistent by locking (exclusive control); locking in turn can cause deadlock, which the DBMS must detect and break.
Databases · AI-written, may contain errors
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