Editing Distributed computing (section)

{{Short description|System with multiple networked computers}}
{{Distinguish|Decentralized computing}}

'''Distributed computing''' is a field of [[computer science]] that studies '''distributed systems''', defined as [[computer system]]s whose inter-communicating components are located on different [[computer network|networked computers]].<ref name="tanenbaum">{{cite book |author1=Tanenbaum, Andrew S. |author2=Steen, Maarten van |title=Distributed systems: principles and paradigms |publisher=Pearson Prentice Hall |location=Upper Saddle River, NJ |year=2002 |isbn=0-13-088893-1 |url=https://www.distributed-systems.net/index.php/books/ds3/ |access-date=2020-08-28 |archive-date=2020-08-12 |archive-url=https://web.archive.org/web/20200812174339/https://www.distributed-systems.net/index.php/books/ds3/ |url-status=live }}</ref><ref name="Distributed Programs 2010 pp. 373–406">{{cite book | title=Texts in Computer Science | chapter=Distributed Programs | publisher=Springer London | publication-place=London | year=2010 | isbn=978-1-84882-744-8 | issn=1868-0941 | doi=10.1007/978-1-84882-745-5_11 | pages=373–406 | quote=Systems consist of a number of physically distributed components that work independently using their private storage, but also communicate from time to time by explicit message passing. Such systems are called distributed systems.}}</ref> 

The components of a distributed system communicate and coordinate their actions by [[message passing|passing messages]] to one another in order to achieve a common goal. Three significant challenges of distributed systems are: maintaining [[Concurrency (computer science)|concurrency]] of components, overcoming the [[clock synchronization|lack of a global clock]], and managing the independent failure of components.<ref name="tanenbaum" /> When a component of one system fails, the entire system does not fail.{{sfn|Dusseau|Dusseau|2016|p=1–2}} Examples of distributed systems vary from [[service-oriented architecture|SOA-based systems]] to [[microservices]] to [[massively multiplayer online game]]s to [[peer-to-peer|peer-to-peer applications]]. Distributed systems cost significantly more than monolithic architectures, primarily due to increased needs for additional hardware, servers, gateways, firewalls, new subnets, proxies, and so on.<ref>{{Cite book |last=Ford |first=Neal |title=Fundamentals of Software Architecture: An Engineering Approach |date=March 3, 2020 |publisher=O'Reilly Media |isbn=978-1492043454 |edition=1st |pages=146–147}}</ref> Also, distributed systems are prone to [[fallacies of distributed computing]]. On the other hand, a well designed distributed system is more scalable, more durable, more changeable and more fine-tuned than a [[monolithic application]] deployed on a single machine.<ref>{{Cite book |title=Monolith to Microservices Evolutionary Patterns to Transform Your Monolith |publisher=O'Reilly Media |isbn=9781492047810}}</ref> According to Marc Brooker: "a system is scalable in the range where [[marginal cost]] of additional workload is nearly constant." [[Serverless computing|Serverless]] technologies fit this definition but the total cost of ownership, and not just the infra cost must be considered.<ref>{{Cite book |title=Building Serverless Applications on Knative |publisher=O'Reilly Media |isbn=9781098142049}}</ref>

A [[computer program]] that runs within a distributed system is called  a '''distributed program''',<ref name="Distributed Programs 2010 pp. 373–406 II">{{cite book | title=Texts in Computer Science | chapter=Distributed Programs | publisher=Springer London | publication-place=London | year=2010 | isbn=978-1-84882-744-8 | issn=1868-0941 | doi=10.1007/978-1-84882-745-5_11 | pages=373–406 | quote=Distributed programs are abstract descriptions of distributed systems. A distributed program consists of a collection of processes that work concurrently and communicate by explicit message passing. Each process can access a set of variables which are disjoint from the variables that can be changed by any other process.}}</ref> and ''distributed programming'' is the process of writing such programs.<ref>{{harvtxt|Andrews|2000}}. {{harvtxt|Dolev|2000}}. {{harvtxt|Ghosh|2007}}, p. 10.</ref> There are many different types of implementations for the message passing mechanism, including pure HTTP, [[remote procedure call|RPC-like]] connectors and [[message-oriented middleware|message queues]].<ref>{{Cite journal|last=Magnoni|first=L.|date=2015|title=Modern Messaging for Distributed Sytems (sic)|journal=Journal of Physics: Conference Series|language=en|volume=608|issue=1|pages=012038|doi=10.1088/1742-6596/608/1/012038|issn=1742-6596|doi-access=free|bibcode=2015JPhCS.608a2038M }}</ref>

''Distributed computing'' also refers to the use of distributed systems to solve computational problems. In ''distributed computing'', a problem is divided into many tasks, each of which is solved by one or more computers,<ref>{{harvtxt|Godfrey|2002}}.</ref> which communicate with each other via message passing.<ref name="Andrews 2000">{{harvtxt|Andrews|2000}}, p. 291–292. {{harvtxt|Dolev|2000}}, p. 5.</ref>