WebWave: Globally Load Balanced Fully Distributed Caching of Hot Published Documents

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WebWave Globally Load Balanced Fully
Distributed Caching of Hot Published Documents

• A. Heddaya and S. Mirdad
• In Proc. 17th IEEE Intl. Conf. on Distributed
  Computing Systems, May 1997
• Network computing Lab. Jinwon Lee

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Contents

• Problem
• Solution approach
• Critics
• Appendix
• TLB (Tree Load Balance)
• Webfold off-line algorithm for optimal TLB
  assignment
• WebWave on-line algorithm for TLB assignment
• Simulation Result
• WebWave Problem

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Problems

• Increasing Internet Demands
• Use multiple server (load balancers)
• Use multiple cache servers
• But how to mange multiple cache servers?
• Global load balancing to maximize throughput.
• Completely distributed by using local information
• Directory service is bottleneck of multiple cache
  server.
• No Lookup cost for replicated copies
• ICP need extra cost

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Solution approaches (1/3)

• Use a routing tree
• Routes from clients to a server form a routing
  tree
• Can be serviced by any node(cache server) en
  route.
• Load balancing in a tree.

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Solution approaches (2/3)

• How can we achieve a load balanced system?
• Constrain Document Caching
• Caching documents in cache server on routing path
• No lookup for find replicated copies
• Use only Neighboring loads
• high loaded than neighboring nodes
• --gt caching documents

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Solution approaches (3/3)

• Determination of Loads
• Measurements of neighboring nodes
• Autonomous load balancing use local information
• Caching documents in cache server on routing path
• No lookup for replicated documents
• Load delegation between caching servers on
  routing path
• Parent overloaded --gt make copies in child cache
• Child overloaded --gt forward request to parent
  node

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Critic

• Strong point
• No lookup for replicated copy, just use local
  information
• Formal definition of TLB
• off-line algorithm (Webfold), on-line algorithm
  (WebWave)
• Weak point
• Globally balanced? --gt Folded balanced
• Over-Simplified (fixed load) simulation
• Read-only copy --gt Consistency problem

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Tree Load Balance (TLB)
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Tree Load Balance (TLB)

• Root load cannot forward requests
• Parent delegates load only to originating child
  server
• Parent can delegate at most forwarded request

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Tree Load Balance (TLB)
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Webfold Algorithm (off-line TLB assignment)

• Partitioning tree into the same load caching
  servers

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Webfold Algorithm
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WebWave (on-line TLB assignment)

• Satisfy TLB constraints

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Simulation Results

• Assumption
• arbitrarily small fraction of load can be
  transferred
• request rate is fixed
• load communication delay is negligible

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Load Diffusion Limitation

• Multiple Documents

• Tunneling
• direct request to parent