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This Concept Map, created with IHMC CmapTools, has information related to: ch13 tran nest, Nested transactions has Advantages Subtransactions may run concurrently with other subtransactions at the same level. this allows additional concurrency in a transaction. when subtransactions run in different servers, they can work in parallel. e.g. consider the branchTotal operation it can be implemented by invoking getBalance at every account in the branch. these can be done in parallel when the branches have different servers Subtransactions can commit or abort independently. this is potentially more robust a parent can decide on different actions according to whether a subtransaction has aborted or not, Nested transactions has transactions may be composed of other transactions several transactions may be started from within a transaction we have a top-level transaction and subtransactions which may have their own subtransactions, Nested transactions has Commitment A transaction may commit or abort only after its child transactions have completed. A subtransaction decides independently to commit provisionally or to abort. Its decision to abort is final. When a parent aborts, all of its subtransactions are aborted. When a subtransaction aborts, the parent can decide whether to abort or not. If the top-level transaction commits, then all of the subtransactions that have provisionally committed can commit too, provided that none of their ancestors has aborted., Nested transactions has To a parent, a subtransaction is atomic with respect to failures and concurrent access transactions at the same level (e.g. T1 and T2) can run concurrently but access to common objects is serialised a subtransaction can fail independently of its parent and other subtransactions when it aborts, its parent decides what to do, e.g. start another subtransaction or give up The CORBA transaction service supports both flat and nested transactions