Isolating Access to Resources
Early in this chapter you saw that a characteristic of a transaction is that it be isolated from the effects of other transactions. Isolation isn’t as rigid a requirement as the other ACID properties so you have some leeway in how it’s enforced in your applications. To reflect this, resource managers support one or more isolation levels. An isolation level describes the extent to which access to a single resource by concurrent transactions is separated.
The need to isolate transactions is best understood when you consider the interactions that can occur between concurrent transactions when they aren’t kept apart. These interactions are called isolation conditions and they consist of dirty reads, nonrepeatable reads, ...
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