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A Scalable Content Addressable Network

A Scalable Content Addressable Network. (Sigcomm 2001) Authors: Sylvia Ratsanamy, Mark Handley, Paul Francis Richard Karp, Scott Shenker Ehsan Foroughi. Outline. Introduction Design Logical Environment Find and Insert Operations Departure and Recovery Improvements. Introduction.

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A Scalable Content Addressable Network

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  1. A Scalable Content Addressable Network (Sigcomm 2001) Authors: Sylvia Ratsanamy, Mark Handley, Paul Francis Richard Karp, Scott Shenker Ehsan Foroughi

  2. Outline • Introduction • Design • Logical Environment • Find and Insert Operations • Departure and Recovery • Improvements

  3. Introduction • Large Scale Addressing/Storage Management • Key Features: • Distributable/Scalable • Fault Tolerance • Fast Access vs. Low Overhead • Hash Tables: How to distribute them?

  4. Basic Design • Logical Hash Space • Keys hash to a d-dimensional Cartesian co-ordinate space on a d-torus • The space is partitioned into distinct zones • Zones are d-dimensional rectangles • Zones are neighbor if share in (d-1) dimention

  5. Y 1.0 0.5 X 0, 0 0.5 1.0 d-dimensional Torus

  6. Routing • Queries are hashed to the space, then routed to the node that handles the destination point on the virtual space • Each node maintains information about its neighbors • Routing is greedy, i.e. the query is forwarded to the neighbor with least distance to destination

  7. Example of Routing

  8. P Split Start to Join Insertion • Find an arbitrary node of the system • Pick a random key and hash it to some point • Find the owner of the zone using the routing mechanism

  9. New Zone Insertion cont’d • Split the destination zone • Take over a half of the new zone • Update the neighbor information lists both on new zones and all neighbors of the old zone

  10. Operation Cost • Average path length is (d/2)(n1/d) hops • Average neighbor list is 2d • Letting d=log n both average path length and neighbor list will be O( log n )

  11. Departure & Recovery • Departure can be • With previous warning • Sudden death • In case of normal departure, the node will explicitly hand out the zone to one of its neighbors and the depart • Under normal conditions, nodes transmit update message so that neighbors will know when someone is dead using a timeout timer and ping!

  12. Recovery • In case of abnormal departure, the neighbors decide who should TAKEOVER the zone (node with smallest zone) • In both case, some nodes may handle more than one zone temporarily • Massive cluster failures can bring CAN to an inconsistent state! (not very probable)

  13. Zone Reassignment • Fragmentation problem due to departure of nodes • A background algorithm reassigns zone and tries to merge-up zones to reduce the number of zones each node handles

  14. Improvements • Multi-Dimension • Metrics • Multi-Coordinate Spaces • Overloading the Zones • Multiple Hash Functions • Topologically Sensitive Construction • Uniform Partitioning • Caching

  15. Conclusion • Drawbacks • Not possible to increase dimension • Physical neighboring vs. logical neighboring • Applications • P2P File Sharing • DNS • …

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