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A Prediction-based Fair Replication Algorithm in Structured P2P Systems Xianshu Zhu, Dafang Zhang, Wenjia Li, Kun Huang Presented by: Xianshu Zhu College of Computer & Communication, Hunan University, P.R.China
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Outline IntroductionContribution PFR (Prediction-based Fair Replication) Performance Evaluation Conclusion and Future Work
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Introduction Query Hotspot Structured Peer-to-Peer Network Summary of Replication Schemes
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Query Hotspot F G I J C D E H B FileFile Query Hotspot: the number of requests for popular objects increases dramatically, and leads to consequent dropping queries and severe performance failures. Query Hotspot
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Structured P2P Network Advantage : - Scalability - Scalability - Efficient Searching - Efficient Searching Disadvantage : The Implementation of Structured P2P Network Assumes that All Data Items are of the Same Popularity. No Mechanism Can Handle Hotspot Problem
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Replication Schemes Basic Idea : - Distribute Replicas of the Popular Data Items to Various Light-loaded Nodes - Distribute Replicas of the Popular Data Items to Various Light-loaded Nodes - Fairly Distribute Load onto Each Node. - Fairly Distribute Load onto Each Node. When Apply Replication Technique: - Replica Creation: Time, Number, Location - Replica Creation: Time, Number, Location - Replica Utilization - Replica Utilization
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Replication Schemes Classification According to Replica Location: - Path Replication - Path Replication - Owner Replication - Owner Replication - Random Replication - Random Replication A BCDEF FileFileFileFileFileFileFileFileFileFileFileFile High Replication Overhead
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Replication Schemes A BCDEF File A 1.New Query Hotspot 2.Low Replication Speed Classification According to Replica Location: - Path Replication - Path Replication - Owner Replication: Gopalakrishnan proposed LAR - Owner Replication: Gopalakrishnan proposed LAR - Random Replication - Random Replication File B File D File B File A
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Replication Schemes A BCDEF FileFileFileFileFileFileFileFile Classification According to Replica Location: - Path Replication - Path Replication - Owner Replication - Owner Replication - Random Replication - Random Replication
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Outline IntroductionContribution PFR (Prediction-based Fair Replication) Performance Evaluation Conclusion and Future Work
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Contribution Design Goals: - Dropped Queries by Only Introducing Minimum Replication Overhead - Dropped Queries by Only Introducing Minimum Replication Overhead - Minimize the Drawbacks of LAR Algorithm (Owner Replication) - Minimize the Drawbacks of LAR Algorithm (Owner Replication) Prediction-based Fair Replication Algorithm (PFR) that Can Almost Fairly Distribute Load onto Each Node, So As to Meet the Above Design Goal.
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Contribution Fairness Goal of PFR -Adaptively Determine the Replication Speed and Replication Location According to Node’s Predicted Load Fraction A BCDEFG
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Outline IntroductionContribution PFR (Prediction-based Fair Replication) Performance Evaluation Conclusion and Future Work
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Predict(n+1) PFR- Appropriate Replication Time To keep the System Performance at a High Level, Preventive Actions Should be Taken Before Query Hotspot Really Happens Period Exponential Weight Prediction Algorithm Predict(n+1)=Current(n) + PredictDiff(n+1) Predict(n+1)=Current(n) + PredictDiff(n+1) 12 nn+1n-1 Current Time Predicted Possible Traffic Difference Between nth and (n+1)th Interval
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Period Exponential Weight Prediction Algorithm - Only Incurs Low Computation Overhead - Only Incurs Low Computation Overhead - Applicable to Online Prediction - Applicable to Online Prediction Our Replication Strategy is Set Based on The Predicted load PFR- Appropriate Replication Time
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Replication Speed: A BCDEF FileFile FileFileFileFileFileFile 3/6 Replication Speed=(the Number of Nodes Chosen to Hold Replicas)/(the Number of All Nodes that Have Encountered Along the Query Path) PFR- Fairly-decided Replication Speed
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Replication Level: NN/2 3N/4 N/4 1 DON’T create replicas N: Total Number of Nodes Along a Query Path PFR- Fairly-decided Replication Speed Replication Speed Predicted Load Fraction (0.5) (0.3) (0.6) (0.7) (0.8) (1) Node Homogeneity
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PFR- Replication & Replica Utilization ABCDEF G C: File F:0.25E:0.15F:0.25 E:0.15 F:0.25D:0.3 C:0.55E:0.15 F:0.25 D:0.3B:0.3C:0.55 E:0.15 F:0.25 D:0.3A:0.9B:0.3 C:0.55 E:0.15 F:0.25 D:0.3 RS:N/4=1 A: File RS:N E:C E:C E:C B,D,E,F:A B,D,E,F:A B,D,E,F:A B,D,E,F:A B,D,E,F:A B,D,E,F:A D:A N=6
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Outline IntroductionContribution PFR (Prediction-based Fair Replication) Performance Evaluation Conclusion and Future Work
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Performance Evaluation Highly modified Chord Simulator from MIT and LAR Implementation Code : Highly modified Chord Simulator from MIT and LAR Implementation Code : System Size 1000 The Time Each Network hop takes 25ms Number of data 32767 Average system load 25% Node capacity 10 per sec Number of Queries Generate per Sec 500 Node’s queue length 32 Prediction interval 1s
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Performance Evaluation Number of Queries Dropped Over Time 28% 90% of the input queries are directed to 1 item LAR PFR
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Performance Evaluation Total Number of Documents Replicated LAR PFR
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Performance Evaluation Total Number of Finger Tables Replicated LAR PFR
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Performance Evaluation Total Number of Replica Location Hints Created PFR LAR
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Outline IntroductionContribution PFR (Prediction-based Fair Replication) Performance Evaluation Conclusion and Future Work
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Conclusion Prediction-based Fair Replication Algorithm Can Conduct Fair Replication through: - Appropriate Replication Time - Appropriate Replication Time - Fairly-decided Replication Speed - Fairly-decided Replication Speed - Fairly-decided Replication Location - Fairly-decided Replication Location - High Replica Utilization Rate - High Replica Utilization Rate Performance Evaluation: - Notably Decrease the Number of Dropped Queries - Notably Decrease the Number of Dropped Queries - Low Replication Overhead - Low Replication Overhead
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Future Work Taking Node Heterogeneity into Consideration
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Thank you!
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