Peer-to-Peer Information Systems Week 6: Performance Old Dominion University Department of Computer Science CS 495/595 Fall 2004 Michael L. Nelson <mln@cs.odu.edu> 10/05/04

Regular & Random Graphs vertices: n=4096 neighbors: k=8 Regular Graph average diameter n/2k clustering coefficient (connections present) / (k(k-1)/2) approaches .75 for large n Random Graph average diameter log(n/log k) clustering coefficient k/n approaches 0 for large n =256 =4 =0.002 =0.5 figures 14-4 & 14-5 from Ch. 14 & http://www.doc.ic.ac.uk/~twh1/academic/papers/oreilly.pdf

Small Worlds, Revisited Duncan J. Watts, Steven H. Strogatz. Collective Dynamics of 'Small-World' Networks. Nature 393, 440-442 (1998) http://dx.doi.org/10.1038/30918 figures 1 & 2 from Watts & Strogatz

Freenet Performance Simulation 1000 identical nodes capacity: n=1000, k=4 diameter = 125, CC=0.5 capacity: 50 data items (all initially empty) 200 references (4 nearest neighbors initially linked) every timestep, randomly pick a node for an insert or request TTL=20 figure 14-8 from Ch. 14 & http://www.doc.ic.ac.uk/~twh1/academic/papers/oreilly.pdf

Freenet Path Evolution approaching 2 figure 14-9 from Ch. 14 & http://www.doc.ic.ac.uk/~twh1/academic/papers/oreilly.pdf

Freenet Path Evolution approaching 6; cf. ~50 for random routing (figure 14-13) figures 14-10 & 14-12 from Ch. 14 & http://www.doc.ic.ac.uk/~twh1/academic/papers/oreilly.pdf

Growing the Freenet Network start with 20 nodes add a new node every 5 timesteps until 1000 nodes results path length 2.2 CC 0.22 50% requests complete in <= 5 hops figure 14-15 from Ch. 14 & http://www.doc.ic.ac.uk/~twh1/academic/papers/oreilly.pdf

Attacks vs. Failures figure 14-19 from Ch. 14 & http://www.doc.ic.ac.uk/~twh1/academic/papers/oreilly.pdf

Free Riders in Freenet No real impact: if you don’t share files, you don’t get linked into the network the free riding node can contribute traffic to the network if a node refuses incoming connections, it is considered “down” and the other nodes route around it

Freenet Scalability slope increase probably due to a simulation side-effect figures 14-21 & 14-22 from Ch. 14 & http://www.doc.ic.ac.uk/~twh1/academic/papers/oreilly.pdf

Gnutella Performance build 1000 empty nodes, randomly add 1500 edges n=1000, k=3 random graph! (cf. Figure 14-5) after initialization, the network does not evolve no adds or joins “publish” 2500 data objects; each exists in 20 locations 50k (2500 * 20) total files in the network perform 300 queries on random files, TTL= halt query after file is found (unlike the real Gnutella)

Gnutella Communication breadth-first search finds the shortest path… figure 3 from Ripeanu, Iamnitchi & Foster, IEEE IC, 6(1), 2002 figures 14-23 from Ch. 14 & http://www.doc.ic.ac.uk/~twh1/academic/papers/oreilly.pdf

Gnutella Communications …but costs communications figure 14-24 from Ch. 14 & http://www.doc.ic.ac.uk/~twh1/academic/papers/oreilly.pdf

Gnutella Attacks vs. Failures no real difference between attacks and failures… …but are assumptions still valid? figures 14-29 & 14-26 from Ch. 14 & http://www.doc.ic.ac.uk/~twh1/academic/papers/oreilly.pdf

Gnutella - Power Law? figures 5&6 from Ripeanu, Iamnitchi & Foster, IEEE IC, 6(1), 2002

Free Riding in Gnutella 73% of Gnutella users share < 10 files! Gnutella has no mechanism to describe or remember “good” hosts free riders increase the path length w/o adding content free riders increase the communications requirements figure 1 from Adar & Huberman, http://www.firstmonday.dk/issues/issue5_10/adar/

Gnutella Scalability cf. figures 14-21 & 14-22 figure 14-31 from Ch. 14 & http://www.doc.ic.ac.uk/~twh1/academic/papers/oreilly.pdf

Super-peers All peers are equal, but some peers are more equal than others Beverly Yang, Hector Garcia-Molina, "Designing a Super-peer Network." In Proceedings of the 19th International Conference on Data Engineering (ICDE), Bangalore, India, March 2003. http://www-db.stanford.edu/~byang/pubs/superpeer.pdf definitions pure P2P: Gnutella, Freenet, Free Haven hybrid P2P: Napster super-peer: a node that acts as a centralized server (hybrid system) to a subset of clients super-peers are connected, and communication between them occurs as a pure P2P for downloads, peer and super-peer distinctions don’t matter

Super-Peer Network

Super-Peer Motivation very heterogeneous capability in P2P systems http://citeseer.nj.nec.com/saroiu02measurement.html combine pure & hybrid capabilities build hierarchical structures? super-super-peer? super-super-super-peer? Super-peer examples: http://www.kazaa.com/ http://www.morpheus.com/ http://www.grokster.com/

Gnutella Reflectors instead of forwarding queries, a Gnutella reflector answers them from its cache resources: http://www.openp2p.com/pub/a/p2p/2001/03/22/truelove.html?page=4 http://web.archive.org/web/20010616055844/http://www.clip2.com/reflector.html also: gnuTellavision http://www.sims.berkeley.edu/~rachna/gtv/ figure from http://web.archive.org/web/20010616055844/http://www.clip2.com/reflector.html

Gnutella Maps from: http://www.cybergeography.org/atlas/more_topology.html; cf. figure 8-3 (p. 109)

Super-Peer Definitions from Yang & Garcia-Molina, 2003 load = f(incoming bandwidth, outgoing bandwidth, processing power) individual load = load of 1 node aggregate load = load of all nodes in system k-redundancy = a super-peer has k backups

Super-Peer Rules of Thumb from Yang & Garcia-Molina, 2003 Increasing cluster size decreases aggregate load, but increases individual load as the cluster size grows, super-peers work harder Super-peer redundancy is good additional complexity, but yields “good aggregate load of a large cluster size, and the good individual load of a smaller cluster size -- in addition to increased reliability” Maximize outdegree of super-peers decreases expected # of hops, provided that all super-peers take on more clients Minimize TTL TTL can be tuned: start high, look at how far away your results are, back down to that…

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