Nested transaction

From Wikipedia, the free encyclopedia

With reference to a database transaction, a nested transaction occurs when a new transaction is started by an instruction that is already inside an existing transaction. The new nested transaction is said to be nested within the existing transaction, hence the term.

Changes made by the nested transaction are not seen by the 'host' transaction until the nested transaction is committed. This follows from the isolation property of transactions.

The capability to handle nested transactions properly is a prerequisite for true component based application architectures. In a component-based, encapsulated architecture, nested transactions can occur without the programmer knowing it. A component function may or may not contain a database transaction (this is the encapsulated secret of the component. See Information hiding). If a call to such a component function is made inside a BEGIN - COMMIT bracket, nested transactions occur. Since popular databases like MySQL do not allow nesting BEGIN - COMMIT brackets, a framework or a transaction monitor is needed to handle this.

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