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Adaptive Configuration of a Web Caching Hierarchy Pranav A. Desai Jaspal Subhlok Presented by: Pranav A. Desai
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Introduction Web caching Used to improve the performance of the World Wide Web Hierarchy of caches Further enhances the performance Goal of the research Improve the performance of a caching hierarchy
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Outline Web caching hierarchy Motivation Approach Adaptive Hierarchy Management System Performance evaluation Conclusion & Future work
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Web Caching Hierarchy A network of cooperating caches hierarchically arranged in a tree-like structure Caches can have sibling-sibling or parent- child relationship with other caches
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Web Caching Hierarchy Child Web Caches Parent Web Cache parent-child relationship sibling-sibling relationship ICP Queries Request to Origin Server
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Motivation Limitations of a caching hierarchy Requires manual configuration Changes in network conditions may deteriorate the performance of the caches in the hierarchy
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Cache A Cache BCache C Example All sibling hierarchy Request Congested network to Origin Server
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Cache A Cache BCache C Example All sibling hierarchy
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Metrics we need to consider Available bandwidth (network metric) Indicative of the overhead associated with cooperating with peer caches Inter-cache hit ratio (cache metric) Measures the benefit due to hierarchy Other metrics that we considered Request hit ratio Request rate CPU load Service time (hits and misses) Round trip time
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Solution Requires two components A mechanism Collect the metrics Reconfigure the caches A policy An algorithm that can design a hierarchy using the metrics
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Cache A Cache BCache C CONTROLLER NW S AGENTS Adaptive Hierarchy Management System
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Adaptive Hierarchy Algorithm The algorithm uses threshold values for the metrics to design the hierarchy The threshold values are determined empirically
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Experimental Setup Experiments are performed on a Squid cache hierarchy of three sibling caches Bandwidth is controlled using Dummynet Client robots send requests from web traces obtained from NLANR (National Laboratory for Applied Network Research) Traces are randomly selected from different sites in the NLANR hierarchy
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Determination of threshold values Traces used are 10000 requests long Bandwidth is varied in step of 100, 10, 1, 0.1 Mbps To simulate realistic conditions the caches are warmed before performing the experiments Sending specific amount of requests to the caches before performing the experiments Three levels of warming – 0%, 50%, 100% Threshold values are determined by comparing the performance of the hierarchies A CB Hierarchy 0 A CB Hierarchy 1
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Impact of Sibling Cache Benefit of hierarchy is not obtained due to high ICP overhead and low inter-cache hit ratio A CB Hierarchy 0 A CB Hierarchy 1
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Impact of Sibling Cache A B Hierarchy 0 A C B Hierarchy 1 C
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Adaptive Hierarchy Algorithm For bandwidths > 10Mbps cooperating with peer caches is beneficial For bandwidths in the range 10 – 1 Mbps communicating with peer cache is beneficial if inter-cache hit ratio > 6% For bandwidth < 1Mbps eliminating the relationship is beneficial in all cases
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Adaptive Hierarchy Algorithm Select a Link BW < 1% of maxBW ? Set Link Relation to NONE 1% < BW < 10% of maxBW ? IC_HR < 6% ? Set Relation to SIBLING Check Link Relation Y Y Y N N NNONE PARENT or SIBLING
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Performance of Adaptive Hierarchy Bandwidth is varied randomly in steps of 100, 10, 1 and 0.1 Mbps The period for each bandwidth phase is controlled Each trace is about half million requests long A CB SiblingSibling Sibling
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MeanMedian Performance with Adaptive Hierarchy Performance improvement of 13% and 29% is obtained in mean response time for cache A and cache B respectively Improvement is not evident from the median response time
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Response time of individual requests
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Conclusion Adaptive Hierarchy Management System is capable of dynamically configuring a set of caches into good hierarchies In our experimental setup Adaptive hierarchy performs better by around 30%
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Future Work Extensive evaluation of the system Evaluation of other metrics Request hit ratio Request rate Service time (Hit and Miss) Round trip time Auto discovery of caches
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Thank You!
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