Lars Bremer and Kalman Graffi. Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case. In IEEE ICC ’13: Proceedings of the International Conference on Communications, 2013. Abstract—Comparative evaluations of peer-to-peer protocols through simulations are a viable approach to judge the per- formance and costs of the individual protocols in large-scale networks. In order to support this work, we enhanced the peer- to-peer systems simulator PeerfactSim.KOM with a fine-grained analyzer concept, with exhaustive automated measurements and gnuplot generators as well as a coordination control to evaluate a set of experiment setups in parallel. Thus, by configuring all experiments and protocols only once and starting the simulator, all desired measurements are performed, analyzed, evaluated and combined, resulting in a holistic environment for the comparative evaluation of peer-to-peer systems. Abstract—Cloud computing offers high availability, dynamic scalability, and elasticity requiring only very little administration. However, this service comes with financial costs. Peer-to-peer systems, in contrast, operate at very low costs but cannot match the quality of service of the cloud. This paper focuses on the case study of Wikipedia and presents an approach to reduce the operational costs of hosting similar websites in the cloud by using a practical peer-to-peer approach. The visitors of the site are joining a Chord overlay, which acts as first cache for article lookups. Simulation results show, that up to 72% of the article lookups in Wikipedia could be answered by other visitors instead of using the cloud.

1. Symbiotic Coupling of P2P and Cloud Systems:
The Wikipedia Case
Lars Bremer, University of Paderborn, Germany
Kalman Graffi, University of Düsseldorf, Germany

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Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 2

3. Background on Wikipedia
Wikipedia
– Collaborative Internet Encylopaedia
Numbers on English Wikipedia
– Alexa rank: 6
– Article Count: 3.8 million
– Edits: 3.4 million per month
– Page Views: 11.3 million per hour
Figures show the popularity of articles
– Top: All articles
– Bottom: Top 250 articles
Problem: Costs through high traffic
Wikipedia: Page View Distribution
Wikipedia: Page View Distribution
0 0 . 5 1 1 . 5 2 2 . 5
1 0 6
1 0 4
1 0 2
1 0 0
1 0 6
1 0 4
1 0 2
1 0 0
1 0 6
1 0 5
1 0 4
1 0 3
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 3
x 1 0 6
1 0
R a n k
P a g e V i e w s
Distribution, All Ranks 0 0 . 5 1 1 . 5 2 2 . 5
x 1 0 6
1 0
R a n k
P a g e V i e w s
0 5 0 1 0 0 1 5 0 2 0 0 2 5 0
1 0 2
R a n k
P a g e V i e w s
Distribution, All Ranks Distribution, First 250 Ranks

4. Motivation and Outline of our Work
Goal: Efficiency increase
– Cloud-like performance
• Maintain high data availability
• Quick article delivery
– Low operational costs
• Users should help in sharing articles
• Donations of network resources
Approach
– Combine peer-to-peer (p2p) and centralized (cloud) architecture
– Cloud is used as backup and main hoster
• Much less traffic and costs
– Users participate in p2p overlay
• Lookup articles first there
• Provide downloaded articles to other peers
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 4

5. Outline
Motivation / Use Case
Background on Structured P2P Overlays
Symbiotic Coupling of P2P and Cloud Systems
Evaluation
Conclusions
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 5

6. Background on Structured P2P Overlays
Nodes and objects use same ID
space
Each object is managed by a
node ( responsible)
Assignment based on IDs
Nodes maintain a topology /
routing structure to support:
Lookup:
getResponsibleNode(ID)
After that: e.g. data tranfer
H(„my data“)
= 3107
1008 1622 2011
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 6
2207
2906
3485
709
611
?
Lookup
Data transfer
Model Overview

7. Cloud Computing vs. P2P Technology
Cloud and P2P
– Access to a distributed pool of
resources:
• Storage, bandwidth, computational
power
Cloud computing
– Resource providers: companies
– Controlled environment
• No (/minimal) churn
• Homogenous devices
– Selective centralized structures
– Mainly paid by usage
P2P systems
– Resource providers: user devices
– Uncontrolled environment
• Churn
• Heterogeneous devices
• Uncertainty / unpredictability
• Distributed access points
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 7

8. Symbiotic Coupling of P2P and Cloud Systems
Goal: High performance at low costs
– Performance: data availability, low delays
– Costs: traffic at cloud operator (linked to monetary expenses)
Our approach
– Main service (here Wikipedia) remains as main data pool
– Nodes install an (p2p) addon  p2p overlay
• Allows to share content of specific services
– Nodes visiting Wikipedia
• Join the p2p overlay and remain online for a while
– Articles are served and provided in p2p overlay
– If not available / initially: download from cloud
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 8

9. Model Overview
Overview on the Architecture
Document space
· Key Idea: References
· All downloaded Articles are published
· Cloud used as Fallback
R E F E R E N C E T A B L E
a r t i c l e n o d e
A 1 N 1
A 1 N 2
A 1 N 4
A 2 N 2
– Article ID is hashed article name
– Responsible node maintains
list of articles providers
– Article providers
• Downloaded once the article
• Registered at resp. node
We use Chord
– Any other DHT also fine
– Needs to support
D O C U M E N T T A B L E
A 1
A 1
N 1
N 2
N 3
N 4
A 2
D O C U M E N T T A B L E
A 1
D O C U M E N T T A B L E
A 1
A 2
Key-based Routing
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 9

10. Operation: Initial Lookup for an Article
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 10

11. Operation: Further Lookup for an Article
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 11

12. Other Operations
Update
– Editing done on the Cloud
– Active vs. passive updates
• Active: Cloud actively informs node holding references
• Passive: Responsible peers periodically check for updates
– Frequency based on object popularity
– Old references are discarded
• They point to outdated content
– New reference table is built-up
Leave
– Leaving node informs all nodes holding references to it
– Can also be detected, but introduces delay
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 12

13. Evaluation
Main questions
– What is the efficiency gain?
– How much traffic is saved?
Approach
– Evaluation through simulation
Layer setup
– User mode: downscaled Wikipedia workload
– Application: document storage
– Overlay: Chord
– Network model:
• Global Network Positioning delay model
• OECD bandwidth model
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 13

14. ► PeerfactSim.KOM (see www.peerfact.org)
Type
– Event-based simulator
– Written in Java
– Simulations up to 100K peers possible
– Focus on simulation of p2p systems on various layers
• User
• Application
• Services: monitoring, replication …
• Overlays
• Network models
Invitation to join the community
– Several universities use and extend the simulator actively
– Used and heavily extended in the project
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 14

15. Layered View
Layered Architecture
– Easy exchange of components
– Testing of new applications
– Testing of new mechanisms
Main idea
– Layers have several implementations
– Enables testing of individual layer
mechanisms
• on its own
• in combination with other layers
See www.peerfact.org
User
Application
Service
Overlay
Simulation Engine
Transport
Network
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 15

16. Simulation Setup / Workload Model
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 16

17. Simulation Results
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
MST 30min, Reference
MST 60min, Reference
MST 90min, Reference
MST 120min, Reference
MST 30min, Article
MST 60min, Article
MST 90min, Article
MST 120min, Article
0 0.2 0.4 0.6 0.8 1.0
Reference Lookup Time (Sec)
All Queries
(a) Reference Lookup and Total Download Time Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 17

18. Simulation Results
1.0
Download Time (b) Traffic Load in the Cloud
0 Articles Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 18
80
70
60
50
40
30
20
10
0
/ min
(c) Traffic

19. Simulation Results
80
70
60
50
40
30
20
10
0
Downloaded from Peer
Downloaded from Cloud
0 20 40 60 80 100 120 140 160 180
Articles / min
Simulation Time (min)
(c) Traffic Load Savings for Session Time 120 min
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 19

20. Conclusions and Future Work
Symbiotic p2p/cloud approach lowers operational costs
– Users take load and share content
– Traffic load on server was reduced to 27.6% in this experiment
– Websites with many users can benefit from p2p support
– WebP2P – browser-based p2p via peerjs, nodejs, etc. is coming
– User devices are powerful, load can be handled „for free“
Future Work
– Investigate WebP2P approach
• Browser plugin to create p2p overlay
– Create p2p framework for social networks
• Use capacity of user devices to host a social network
• See http://www.p2pframework.com
– Further extend PeerfactSim.KOM – the p2p system simulator
• See http://www.peerfact.org
Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 20

21. Thank You for Your Attention
Jun.-Prof. Dr.-Ing. Kalman Graffi
Technology of Social Networks Group
Institute of Computer Science
Heinrich-Heine-Universität Düsseldorf
eMail: graffi@cs.uni-duesseldorf.de
Web: www.p2pframework.com
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Lars Bremer, Kalman Graffi: Symbiotic Coupling of P2P and Cloud Systems: The Wikipedia Case 21