Multi-level transaction schedulers adapt conflict-serializability on different levels. They exploit the fact that many low-level conflicts (e.g. on the level of pages) become irrelevent, if higher-level application semantics is taken into account. Multi-level transactions may lead to an increase in concurrency. It is easy to generalize locking protocols to the case of multi-level transactions. It will be shown that strict 2-PL always leads to serializable, strict schedules. However, the possibility of deadlocks may diminish the increase in concurrency. This stimulates the investigation of optimistic or hybrid approaches to concurrency control. The FoPL protocol is a hybrid concurrency control protocol for multi-level transactions. It employs access lists on the database objects and forward oriented commit validation. The basic test on all levels is based on the recordering of the access lists. When combined with queueing and deadlock detection, the protocol is not only sound, but also complete for multi-level serializable schedules. This is definitely an advantage of FoPL compared with locking protocols. A disadvantage is that strictness is not achievable, but only recoverability. The basic FoPL protocol can be optimized in various ways. In order to investigate the potential of both locking protocols. (orig.)SIGLEAvailable from TIB Hannover: RR 4485(1999,19) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
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