Locality Optimizations in Tapestry
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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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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


Object location in tapestry

Berkeley

MIT

Object Location in Tapestry

UW


Is this always optimal

Berkeley

MIT

Is This Always Optimal?

UW


Locality optimizations in tapestry

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


Locality optimizations in tapestry

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


Locality optimizations in tapestry

Optimization 1: Publish to Backups

Experiments run in simulation on a PlanetLab-based topology


Optimization 2 local misroute

Berkeley

MIT

Optimization 2: Local Misroute

UW


Locality optimizations in tapestry

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


Locality optimizations in tapestry

Optimization 2: Local Misroute

Experiments run in simulation on a transit-stub topology

“Using sim knowledge” indicates direct use of the topology file


Locality optimizations in tapestry

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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