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Locality Optimizations in Tapestry

Locality Optimizations in Tapestry. Jeremy Stribling Joint work with : Kris Hildrum Ben Y. Zhao Anthony D. Joseph John D. Kubiatowicz Sahara/OceanStore Winter Retreat January 14, 2003. Berkeley. MIT. Object Location in Tapestry. UW. Berkeley. MIT. Is This Always Optimal?. UW.

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Locality Optimizations in Tapestry

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  1. Locality Optimizations in Tapestry Jeremy Stribling Joint work with: Kris Hildrum Ben Y. Zhao Anthony D. Joseph John D. Kubiatowicz Sahara/OceanStore Winter Retreat January 14, 2003

  2. Berkeley MIT Object Location in Tapestry UW

  3. Berkeley MIT Is This Always Optimal? UW

  4. Why Is This a Problem? • Example Application: OceanStore web caching • If a nearby replica exists, we must find it quickly • Measure of Locality: Relative Delay Penalty (RDP) • The ratio of the distance of an object in Tapestry to the minimum possible distance (i.e. over IP) • Problem: finding nearby objects incurs a high RDP • Two extra hops have a huge relative impact if object is close • An issue for all similar systems, not just Tapestry • Solution: trade storage overhead for low RDP

  5. MIT Optimization 1: Publish to Backups • Redundancy: Routing table entries store up to c nodes • Closest node is the primary neighbor, c–1 nodes are backups • A simple optimization: publish to k backups • Limit to the first n hops of the publish path • Result • Nodes near the object more likely to encounter pointers while routing to the root • Storage overhead: k*n additional pointers per object

  6. Optimization 1: Publish to Backups Experiments run in simulation on a PlanetLab-based topology

  7. Berkeley MIT Optimization 2: Local Misroute UW

  8. Optimization 2: Local Misroute • Solution: Before taking “long” hop, misroute to closer node • Look a little harder in the local area before leaving • When publishing, place a pointer on local surrogate • Issue: What determines a “long” hop? • One metric: if next hop is more than m times longer than last hop, consider it “long” • Call m the threshold factor

  9. Optimization 2: Local Misroute Experiments run in simulation on a transit-stub topology “Using sim knowledge” indicates direct use of the topology file

  10. Future Work • Analyze more locality optimizations and different parameter configurations • Take measurements on PlanetLab • Test optimizations with real workloads (i.e. web caching) • Complete cost analysis of storage overhead vs. RDP benefit across all optimizations

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