What is a Distributed System CS4513 Distributed Systems

What is a Distributed System? CS-4513 Distributed Systems Hugh C. Lauer Slides include materials from Modern Operating Systems, 3 rd ed. , by Tannenbaum, Operating System Concepts, 7 th ed. , by Silbershatz, Galvin, & Gagne, Distributed Systems: Principles & Paradigms, 2 nd ed. By Tanenbaum and Van Steen, and Distributed Systems: Concepts and Design, 4 th ed. , by Coulouris, et. al. CS-4513, B-Term 2010 What is a Distributed System? 1

Class Discussion (laptops closed, please) What is Distributed Computing? CS-4513, B-Term 2010 What is a Distributed System? 2

Distributed System • Collection of computers (or processes) that are connected together and (sometimes) interact • Many independent problems at same time • Similar • Different • Or … – One very big problem (or a small number) • Computations that are physically separated • Client-server • Inherently dispersed computations CS-4513, B-Term 2010 What is a Distributed System? 3

Distributed Computing Spectrum • Many independent computations at same time • Similar — e. g. , banking & credit card; airline reservations • Different — e. g. , university computer center; your own PC • Or … – One very big problem (or a few) • Computations that are physically separated • Client-server • Inherently dispersed computations CS-4513, B-Term 2010 What is a Distributed System? 4

Multiprocessing Distributed Computing Spectrum • Many independent problems at same time • Similar — e. g. , banking & credit card; airline reservations • Different — e. g. , university computer center; your own PC • Or … – One very big problem (too big for one computer) • Weather modeling, Finite element analysis; Drug discovery; Gene modeling; Weapons simulation; etc. • Computations that are physically separated • Client-server • Inherently dispersed computations CS-4513, B-Term 2010 What is a Distributed System? 5

Multiprocessing Distributed Computing Spectrum • Many independent problems at same time • Similar — e. g. , banking & credit card; airline reservations • Different — e. g. , university computer center; your own PC • Or… – One very big problem (too big for one computer) • Weather modeling, Finite element analysis; Drug discovery; Gene modeling; Weapons simulation; etc. • Computations that are physically separated • Client-server • Dispersed – routing tables for internet; electric power distribution. CS-4513, B-Term 2010 What is a Distributed System? 6

Observation • Same spectrum applies to multiprocessor systems – Much more tightly coupled that traditional “distributed systems” • Some differences – “Multiprocessor systems” • Usually under same management, often in same room • Very fast communication – “Distributed systems” • Sometimes not under same management • Slower communication CS-4513, B-Term 2010 What is a Distributed System? 7

Another Observation (attributed to R. Hamming) • When you change the operating point of a system by an order of magnitude … … you introduce qualitative changes in how to approach problems CS-4513, B-Term 2010 What is a Distributed System? 8

Observation • Same spectrum applies to multiprocessor systems – Much more tightly coupled that traditionalalitative qu a “distributed systems” s i e e r w e h w t o h So n i e c • Some differences n o w t e iffere s d the h – “Multiprocessor systems” c a s pro m p e a t s • Usually under same management s of sy kind • Very fast communication – “Distributed systems” • Sometimes not under same management • Slower communication CS-4513, B-Term 2010 What is a Distributed System? 9

Let’s look at an example • An inherently distributed computation – I. e. , parts of the computation must occur at physically separate locations – Under separate administrations • Internet routing tables CS-4513, B-Term 2010 What is a Distributed System? 10

The Internet • A vast collection of independent computers – ~ 6 108 — 109 • All connected together • Any computer can send a message to any other • Messages broken up into little packets • Question: how do packets find their way to destinations? CS-4513, B-Term 2010 What is a Distributed System? 11

Internet CS-4513, B-Term 2010 What is a Distributed System? 12

Distributed routing algorithm (naïve simplification) • Each node “knows” which networks are directly connected to it. • Each node maintains table of distant networks • [network #, 1 st hop, “distance”] • Adjacent nodes periodically exchange tables • Update algorithm (for each network in table) • If (my distance to network > neighbor’s distance to network + my distance to neighbor), then … • … update my table entry for that network so that neighbor is first hop. CS-4513, B-Term 2010 What is a Distributed System? 13

Distributed Routing Algorithm (result) • All nodes in Internet maintain reasonably up-to-date routing tables • Rapid responses to changes in network topology, congestion, failures, etc. • Very reliable with no central management! CS-4513, B-Term 2010 What is a Distributed System? 14

Characteristic • The routing algorithm is inherently distributed • Different parts execute in physically separated locations • Only nearby nodes “know” whether – Neighbors are up or down – Networks are congested or not CS-4513, B-Term 2010 What is a Distributed System? 15

Big networks • Network management systems • Monitoring health of network (e. g. , routing tables) • Identifying actual or incipient problems • Data and statistics for planning purposes CS-4513, B-Term 2010 What is a Distributed System? 16

Questions? Next Topic CS-4513, B-Term 2010 What is a Distributed System? 17