p2p-approximately - Scaling Problem Millions of clients...

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Peer-to-Peer 15-441 2 Scaling Problem Millions of clients ! server and network meltdown 3 P2P System Leverage the resources of client machines (peers) Computation, storage, bandwidth 4 Why p2p? Scaling: Create system whose capacity grows with # of clients - automatically! Self-managing This aspect attractive for corporate/datacenter needs e.g., Amazon ! s 100,000-ish machines, google ! s 300k+ Harness lots of “spare” capacity at end-hosts Eliminate centralization Robust to failures, etc. Robust to censorship, politics & legislation?? Create apps/services without having huge resources
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5 Today ! s Goal p2p is hot. There are tons and tons of instances But that ! s not the point Identify fundamental techniques useful in p2p settings Understand the challenges Look at the (current!) boundaries of where 2p is particularly useful 6 Outline p2p file sharing techniques – Downloading: Whole-file vs. chunks – Searching Centralized index (Napster, etc.) Flooding (Gnutella, etc.) Smarter flooding (KaZaA, …) Routing (Freenet, etc.) Uses of p2p - what works well, what doesn ! t? – servers vs. arbitrary nodes – Hard state (backups!) vs soft-state (caches) • Challenges 7 Searching & Fetching Human: “I want to watch that great 80s cult classic " Better Off Dead ! 1. Search: “better off dead” -> better_off_dead.mov or -> 0x539fba83ajdeadbeef 2. Locate sources of better_off_dead.mov 3. Download the file from them 8 Searching Internet N 1 N 2 N 3 N 6 N 5 N 4 Publisher Key=“title” Value=MP3 data… Client Lookup(“title”) ?
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9 Search Approaches • Centralized • Flooding A hybrid: Flooding between “Supernodes” • Structured 10 Different types of searches Needles vs. Haystacks – Searching for top 40, or an obscure punk track from 1981 that nobody ! s heard of? Search expressiveness – Whole word? Regular expressions? File names? Attributes? Whole-text search? (e.g., p2p gnutella or p2p google?) 11 Framework Common Primitives: Join : how to I begin participating? Publish : how do I advertise my file? Search : how to I find a file? Fetch : how to I retrieve a file? 12 Centralized Centralized Database: Join : on startup, client contacts central server Publish : reports list of files to central server Search : query the server => return node(s) that store the requested file
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13 Napster Example: Publish I have X, Y, and Z! Publish insert(X, 123.2.21.23) ... 123.2.21.23 14 Napster: Search Where is file A? Query Reply search(A) --> 123.2.0.18 Fetch 123.2.0.18 15 Napster: Discussion • Pros: – Simple – Search scope is O(1) for even complex searches (one index, etc.) – Controllable (pro or con?) • Cons: – Server maintains O(N) State – Server does all processing – Single point of failure Technical failures + legal (napster shut down 16 Searching Wrap-Up Type O(search) storage Fuzzy?
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