IT arhitektuur
·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.
·Lock manager grants lock if request does not conflict with already granted locks.
·Two phase locking guarantees serialisability.
Deadlock
annaabi.ee 
