CS Professional · Artificial Intelligence, Data Analytics and Cyber Security - Laws and Practice · Database Management
A bank's employee, while a transaction updating a customer's balance is still uncommitted, is shown by another session a balance value that is later rolled back. Under the standard SQL concurrency problems, this anomaly is called:
This is a dirty read. One transaction reads data modified by another transaction that has not committed, and that data is later rolled back, so the reader has seen a value that never officially existed. Proper isolation levels prevent it.
- ADirty readCorrect
- BLost update
- CPhantom deletion
- DDeadlock
Explanation
A dirty read occurs when one transaction reads data written by another transaction that has not yet committed and that is later rolled back. A lost update involves two writes overwriting each other, and a deadlock is mutual waiting for locks.
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