Isolation Phenomena

Dirty reads

  • Reading changes in t2 from t1 before its committed

Lost updates

  • Changes by t1 are lost due to updates from t2

Non repeatable reads

  • Repeated reads of the same record in one transaction results in different values. Happens at "

dirty read A transaction reads data written by a concurrent uncommitted transaction.

nonrepeatable read A transaction re-reads data it has previously read and finds that data has been modified by another transaction (that committed since the initial read).

phantom read A transaction re-executes a query returning a set of rows that satisfy a search condition and finds that the set of rows satisfying the condition has changed due to another recently-committed transaction.

serialization anomaly The result of successfully committing a group of transactions is inconsistent with all possible orderings of running those transactions one at a time.