"subtransactionsare" - 1 õppematerjal

IT arhitektuur

·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.) ­Transaction Monitors (CICS, etc) ·Concurrent processes acquire locks on shared resources from lock manager. ·The principal component that implements 2PL is a lock manager from which concurrent processes or threads acquire locks on every shared resource they access.