Phenomena - Data problem (Concurrency Problem)


Because of a race condition, when several transactions concurrently read from and write to a file, variable or database, the following data problems called phenomena can arise:

The isolation levels are defined in terms of this phenomena (problem) that must be prevented between concurrently executing transactions.


Dirty reads

A transaction reads data that has been written by another transaction that has not been committed yet.

See Dirty read

Non repeatable (fuzzy) reads

A user queries a row and then later queries the same row, only to discover that the data has changed.

See Fuzzy reads (Non repeatable read)

Phantom reads

A transaction reruns a query returning a set of rows that satisfies a search condition and finds that another committed transaction has inserted additional rows that satisfy the condition.

Phantom read/update problem

Dirty Write

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