Top Document: Comp.os.research: Frequently answered questions [3/3: l/m 13 Aug 1996] Previous Document: [1.5.1.1] Strictly consistent systems Next Document: [1.5.1.3] Application-specific coherence See reader questions & answers on this topic! - Help others by sharing your knowledge From: Distributed systems Permitting temporary inconsistencies is a common method of increasing performance in distributed systems. Memory is said to be loosely coherent if the value returned by a read operation is the value written by an update operation to the same object that `could' have immediately preceded the read operation in some legal schedule of the threads in execution [Bennett et al., 90]. Using loose coherence, more than one thread may have write access to the same object, provided that the programmer knows that the writes will not conflict. Another memory consistency model is `release consistency' [Gharachorloo et al., 90], in which memory accesses are divided into ordinary and synchronisation-related accesses. The latter are further divided into `acquire' and `release' operations. The `acquire' operation indicates that shared data is needed, and a processor's updates are not guaranteed to be performed at other nodes until a `release' is performed. The primary advantage of this form of consistency is that it allows consistency updates to be tied to synchronisation events, and therefore to be delayed until actually needed by applications. However, most release consistent systems require the programmer to make explicit use of `acquire' and `release' operations. A DSM system called Midway introduces another new consistency model, `entry consistency' [Bershad et al., 93]. Entry consistency is weaker than many of the other models suggested, including release consistency; it requires explicit annotations to associate synchronisation objects and data. On an `acquire', only the data associated with the synchronisation object is guaranteed to be consistent. This extra weakness permits higher performance implementations of the underlying consistency protocols to be written. Midway also supports stronger consistency models, so that the application programmer can trade-off performance against the extra effort required to write entry consistent programs. User Contributions: 1 UoowNen ⚠ Sep 24, 2021 @ 7:07 am buy zithromax online https://zithromaxazitromycin.com/ - buy zithromax online zithromax online https://zithromaxazitromycin.com/ - buy zithromax Comment about this article, ask questions, or add new information about this topic:Top Document: Comp.os.research: Frequently answered questions [3/3: l/m 13 Aug 1996] Previous Document: [1.5.1.1] Strictly consistent systems Next Document: [1.5.1.3] Application-specific coherence Part1 - Part2 - Part3 - Single Page [ Usenet FAQs | Web FAQs | Documents | RFC Index ] Send corrections/additions to the FAQ Maintainer: os-faq@cse.ucsc.edu
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