隨著網際網路(Internet)的發展，由於易學易用、資料繁多，全球資訊網（World Wide Web，WWW）儼然以成為最多人所使用的服務。甚至有許多人是為了使用全球資訊網上所提供的服務才開始使用網路的。但是，隨著愈多人使用服務，單一的伺服器已無法滿足使用者的需求。為了服務日益增加的使用者，多伺服器的網站叢集（Web Cluster）因此應運而生。並且有許多人為了更有效率的利用網站叢集，而不斷提出新的負載平衡技術(Load Balancing)以滿足更多的使用者。然而負載平衡並不完全等同服務品質(Quality of Service)。使用者除了要求能迅速回應外，也需要能保證從事特定活動時的正確性。因此本研究提出了使用Session的服務品質機制。由我們的實驗結果得知，在犧牲少許效能(Throughput)的狀況下（約減少6%），我們可以降低伺服器的回應時間（約17%）並保證完成有意義的瀏覽行為。我們相信這種機制可以提昇顧客滿意度。

With the development of Internet, WWW (World Wide Web) has become the most popular service in our daily life. However, as the number of users increases, the more computing capabilities such as CPU power and memory capacity are required. However, hardware upgrade is too expensive to solve this problem. Recently, many load-balancing methods are proposed in order to improve performance requirement. They indeed solve this problem. However, there is a more important thing - users need QoS (Quality of Service). In this thesis, we propose a session mechanism of QoS to assure that some important activities must be done completely. Our experiment results show that our new mechanism can shorten response time (about 17%) by only sacrificing little throughput (about 6%). We believe that our mechanism can satisfy customers’ requirements.

Table of Contents

Abstract (in Chinese) i
Abstract ii
Acknowledgement vi
Table of Contents iv
Table of Tables vi
Table of Figures vii
Chapter 1 Introduction 1
1.1 Motivation 1
1.2 Thesis Organization 2
Chapter 2 Cluster-based Web System and QoS 3
2.1 Caching System 3
2.1.1 Proxy Caches 3
2.1.2 Transparent Caches 4
2.1.3 Reverse Proxy Caches 5
2.2 Load Balancing 5
2.2.1 Locations of Servers 5
2.2.2 Master of Load Balancing 7
2.2.3 Implementation of Load Dispatcher 9
2.2.4 Packet Transfer Techniques 11
2.2.5 Scheduling Algorithms 13
2.3 Quality of Service 14
2.3.1 Server-based WQoS 15
2.3.2 Session-based WQoS 17
Chapter 3 System Architecture 19
3.1 Linux Virtual Server 19
3.2 Conception 20
3.3 System Implementation 22
Chapter 4 Experiment Results 24
4.1 Experiment Environment 24
4.2 Apache Flood and Testing Files 25
4.3 Impacts of Session 27
4.4 Choosing Load Threshold 30
4.5 Effect of WQoS 32
Chapter 5 Conclusions and Future Work 36
References 37
Appendix A Testing Profiles I
Appendix B Source Codes and Others III

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