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CSE 291 System Services for the World Wide Web

CSE 291 System Services for the World Wide Web. Winter 2000 Geoffrey M. Voelker. Class Goal. Provide background for doing experimental systems research in wide-area systems such as the Web Architectures for wide-area distributed systems

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CSE 291 System Services for the World Wide Web

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  1. CSE 291System Services for the World Wide Web Winter 2000 Geoffrey M. Voelker

  2. Class Goal • Provide background for doing experimental systems research in wide-area systems such as the Web • Architectures for wide-area distributed systems • What are good models for structuring systems to support apps? • Understanding system behavior • What are the workloads? • Enhancing performance • Caching, prefetching • New opportunities • Multimedia, XML • Read, evaluate, present a variety of research papers • Do projects on interesting problems in area CSE 291 Intro

  3. Today • Course structure • Presentations • Evaluations • Projects • Course contents • Web intro • Topics and papers CSE 291 Intro

  4. Presentations • We will present papers in class for discussion • Roughly 2 papers per 1.5 hour class (sometimes 3) • Everyone presents (including me) • How many depends on # students registered • I will present Thursday’s papers and do my share during the rest of the quarter • Look over schedule between now and Thursday • We’ll allocate papers on Thursday CSE 291 Intro

  5. Evaluations • You must submit evaluations of papers • Email them to me by noon of day of class • No evals if you have to present • Brief (½ page) • Summary of paper (research problem, conclusions) • What you learned • Any ideas that occurred to you • Your frank opinion of topic and/or work • If this gets to be too burdensome, might notch it down to one evaluation per day CSE 291 Intro

  6. Class Participation • The presentations are for fostering discussion …so I expect you to participate in discussions • Presenters • Come prepared with discussion questions • Rest of us • Use your evaluations as a basis for discussion CSE 291 Intro

  7. Class Project • For those signed up for four units • Work in pairs • Schedule in handout, on the Web • Roughly 5 weeks setup, 5 weeks working • Start thinking about what you might want to work on, who you might want to work with • I’ll have a list of topics, but I also encourage you to use your own • Your final will be a class presentation on your project CSE 291 Intro

  8. Course Contents • Topics • Wide-area system architectures • Naming • Scalable servers • Workload characterizations • Caching, prefetching • Protocols • Security • Emerging applications • Overview of Web to help put things into context CSE 291 Intro

  9. How does the Web work? • The canonical example in your Web browser Click here • “here” is a Uniform Resource Locator (URL) http://www-cse.ucsd.edu • It names the location of an object on a server CSE 291 Intro

  10. Client Server In Action… • Client resolves name of server (www-cse.ucsd.edu) • Establishes a connection with the server • Sends the server the name of the object (null) • Server returns the object http://www-cse.ucsd.edu HTTP CSE 291 Intro

  11. Naming • How should objects be named? • URLs name locations…if an object moves, the URL breaks • Location-independent names seem like the obvious way to go • Why don’t we use them (e.g., URIs)? • How do we make them work, esp. in the face of mobility? • How it works now, how it might work in the future • DNS [Mockapetris88] • DNS for URIs [Daniel96] • Names as programs [Vahdat99] • Finding replicas [Guyton95], [vanSteen98] CSE 291 Intro

  12. Client Server Communication • Communication between the client and server is done via HTTP over TCP/IP http://www-cse.ucsd.edu HTTP CSE 291 Intro

  13. Protocols • What kind of transport protocol should the Web use? • HTTP 1.0 • One TCP connection/object • Complaints: inefficient, slow, burdensome… • HTTP 1.1 • One TCP connection/many objects (persistent connections) • Solves all problems, right? Huge amount of complexity • Clients, proxies, servers • How do they compare? • Protocol differences [Krishnamurthy99], performance comparison [Nielsen97], effects on servers [Manley97], overhead of TCP connections [Caceres98] CSE 291 Intro

  14. Scalable Servers • Of course, you are not the only person accessing the server… Server CSE 291 Intro

  15. Scalable Servers • How do you build servers to handle millions of hits a day? • Web servers: Flash [Pai99], scheduling [Crovella99] • Mail servers: EarthLink [Christenson97, Saito99] • Principles: Transcend, HotBot [Fox97] • Techniques: Load balancing [Pai98] CSE 291 Intro

  16. Clients Proxy Cache Servers Web Caching • Gee, is there some way to offload those busy servers? • Use caches to exploit reference locality among clients CSE 291 Intro

  17. Caching • How should we build caching systems for the Web? • Seminal paper [Chankhunthod96] • Proxy caches [Duska97] • Akamai hack [Karger99] • Cooperative caching [Tewari99, Fan98, Wolman99] • Popularity distributions [Breslau99] CSE 291 Intro

  18. Prefetching • The fastest way to download a page is to fetch it before it is accessed • How do you know what will be accessed? • How much bandwidth can you afford for mistakes? • Performances bounds [Kroeger97] • Survey paper w/ practical approach [Duchamp99] CSE 291 Intro

  19. Security • We can’t just assume we’re in a back room anymore • How do we secure access to resources? • Infrastructure: SDSI [Rivest96] • Wide-area service: CRISIS [Belani98] • Computational grids: Globus [Foster98] • E-commerce: SSL [Wagner96] • Downloaded code: Java [Wallach97] CSE 291 Intro

  20. Workload Characterizations • How can you fix it if you don’t look inside? • Is the Web slow because of the network, the server, CPU-hogging browsers? • What is the behavior of clients, proxies, and servers? • Golden fleece: Invariants across populations and time • E.g., Zipf-like distribution of object popularities • How can we use workloads to shape the systems we design? • Characterization survey [Pitkow98] • Rate of change [Douglis97] • Key to data dissemination (caching, prefetching, etc.) CSE 291 Intro

  21. Emerging Applications • HTML, gif, jpeg, etc. are all old news • What’s the new, cool stuff? • Multimedia • Streaming multimedia next big thing (20% b/w in UW traces) • Workloads [Mena00], tools [Caceres99], delivery [Eager00] • XML • I don’t know what it is, so I’d like to learn • Papers TBD CSE 291 Intro

  22. Architectures • The Web is basically a simple read-only data access system • Click, fetch, click, fetch, click, fetch… • Why not fully generalize it into a universal wide-area distributed system? • The Web as an operating system: WebOS [Vahdat98] • Wide-area computational grids: Legion [Lewis96, Grimshaw98], Globe [vanSteen97], Globus [Foster97, Foster98] CSE 291 Intro

  23. Hits Misses Misses Clients Proxy Cache Servers CSE 291 Intro

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