Free Transactions and concurrency lessonsTransactions and concurrency · Stage 1 · Many users at once · Step 2
Isolation levels and anomalies
Meet the four classic anomalies, and the isolation levels that trade correctness against concurrency. About 15 minutes.
A report reads the same row twice in one transaction and gets different values. Which anomaly is this, and which level prevents it?
- AA non-repeatable read; repeatable read (and above) prevents it
- BA dirty read; read committed prevents it
- CA phantom; only serializable prevents it
Show the answer
A non-repeatable read; repeatable read (and above) prevents it. Another transaction updated and committed the row between the two reads.
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