slides.0315 - P2PApps 1 Presentedby KevinLarson &...

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Presented by Kevin Larson Will Dietz 1 P2P Apps
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P2P In General 2 Distributed systems where workloads are partitioned  between peers Peer: Equally privileged members of the system In contrast to client-server models, peers both  provide and consume resources. Classic Examples: Napster Gnutella
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P2P Apps 3 CoDNS Distribute DNS load to other clients in order to greatly reduce  latency in the case of local failures  PAST  Distribute files and replicas across many peers, using diversion  and hashing to increase utilization and insertion success UsenetDHT Use peers to distribute the storage and costs of the Usenet  service
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OSDI 2004 Princeton KyoungSoo Park Zhe Wang Vivek Pai Larry Peterson 4 CoDNS
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What is DNS? 5 Domain Name System Remote server Local resolver  Translates hostnames into IP addresses Ex: www.illinois.edu -> 128.174.4.87 Ubiquitous and long-standing: Average user not  aware of its existence Desired Performance, as observed PlanetLab nodes at Rice and University of Utah
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Environment and Workload 6 PlanetLab  Internet scale test-bed Very large scale Geographically distributed CoDeeN Latency-sensitive content delivery network (CDN) Uses a network of caching Web proxy servers Complex distribution of node accesses + external accesses Built on top of PlanetLab Widely used (4 million plus accesses/day)
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Observed Performance  7 Cornell University of Oregon University of Michigan University of Tennessee
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Traditional DNS Failures 8 Comcast DNS failure Cyber Monday 2010 Complete failure, not just high latency Massive overloading
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What is not working? 9 DNS lookups have high reliability, but make no  latency guarantees: Reliability due to redundancy, which drives up latency Failures significantly skew average lookup times Failures defined as: 5+ second latency – the length of time where the system will  contact a secondary local nameserver No answer
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Time Spent on DNS lookups 10 Three classifications of lookup times:  Low: <10ms  Regular: 10ms to 100ms  High: >100ms High latency lookups account for 0.5% to 12.9% of  accesses 71%-99.2% of time is spent on high latency lookups
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Suspected Failure Classification 11 Cornell University of Oregon University of Michigan University of Tennessee Long lasting, continuous failures:  - Result from nameserver failures  and/or extended overloading Short sporadic failures:  - Result from temporary  overloading Periodic Failures – caused by cron  jobs and other scheduled tasks
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CoDNS Ideas 12 Attempt to resolve locally, then request data from  peers if too slow
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slides.0315 - P2PApps 1 Presentedby KevinLarson &amp;...

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