"subtransactionscan" - 1 õppematerjal

IT arhitektuur

inconsistency. ­The parent transaction then continous at the point where the aborted subtransactionwas started. ·To start a subtransaction, transactional clients invoke a begin transaction operation from the transaction coordinator during the course of a parent transaction. ·With nested transactions it is, therefore, permitted to have a begin transaction operation without having completed the previous transaction and such a begin will launch a subtransaction. ·Subtransactionscan have subtransactionsof their own, leading to an arbitrary deep nesting hierarchy. ·If a parent transaction is aborted, however, the effect of all its completed subtransactionsis undone. ·Consequently, if the root transaction is aborted all commited subtransactionsare undone. 21. Two Phase Locking (2PL), Deadlocks 2PL ·The most popular concurrency control technique. Used in: ­RDBMSs(Oracle, Ingres, Sybase, DB/2, etc.) ­ODBMSs (O2, ObjectStore, Versant, etc.)