Demystifying Database Systems: An Introduction to Transaction Isolation Levels

Nonetheless, many database users stick with the default isolation level of whatever database system they are using, and do not bother to consider which isolation level is optimal for their application. We defined isolation above as the ability of a database system to allow a transaction to execute as if there are no other concurrently running transactions (even though in reality that can be a large number of concurrently running transactions). If the application developer is able to ensure the correctness of their code when no other concurrent processes are running, a system that guarantees perfect isolation will ensure that the code remains correct even when there is other code running concurrently in the system that may read or write the same data.

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