隨著網際網路快速普及，許多服務逐漸由傳統型態轉變以網頁服務作為媒介。單一網頁伺服器架構已無法滿足如此龐大的使用者需求，叢集式網頁伺服器架構儼然成為另一個合適的解決方案。分配機制在叢集式Web伺服器中扮演一個非常重要的角色，因此過去幾年間有許多負載平衡分配策略被發展出來，然而這些研究都只有以模擬系統來加以驗證，因此這些策略在一個真實的系統中運作的效能為何仍屬未知。在這些模擬系統中，過去的研究都假設Web的流量遵循一定的分佈（一般稱之為heavy-tailed），然而經由過去幾年我們實際維運一個Web cluster的經驗來看，我們發現這樣的假設已有所改變。就目前的網頁內容來看，Web檔案平均大小有變大的趨勢，主要的原因是這幾年網路技術快速進步，頻寬不斷的被增加，使得許多豐富的多媒體內容變為可行，藉由網路作為媒介，一些資訊紛紛上網，如：線上學習系統中的大量的教學影音檔或教材、軟體公司的修補檔(patch)或試用版(trial)軟體、遊戲公司的試玩版遊戲等。我們稱這樣的Web流量為data-intensive的workload。
基於上述的問題，本文主要著重於了解以往所被提出的各種分配服務請求策略，在真實環境中運作的情形，我們在一個實際運作中的叢集式Web伺服器系統上實做了各種分配機制，並進而設計實驗方法以實際的data-intensive Web流量來比較與分析這幾個分配策略的優劣。

The Internet has become popular and many traditional services have changed into web service stage by stage. The web server with single architecture is no longer satisfying a large number of user requests and the cluster-based web server architecture becomes another suitable solution. Dispatch mechanism play an important role in web server cluster and there are many load balancing policies have been proposed recently. But, these research has only simulation, performance of these policies operate in a real system is unknown. In these simulation all has an assumption that web traffic is heavy-tailed distribution. However, in our experience, the assumption has changed. Web content has become large because network bandwidth increasing and more and more large files like video、audio and tail software, etc. coming in. We defined this web traffic is a data-intensive workload.
In this study, we use a real and data-intensive web site to measure and compare these scheduling policies.

圖表目錄 6
第一章、 緒論 8
1.1研究背景 8
1.2研究動機與目的 9
1.3章節導讀 10
第二章、 背景知識與相關研究 11
2.1 World Wide Web 11
2.2 How does Web work 12
2.3 Web-Server Cluster 14
2.4 How does Web-Server Cluster work 15
2.5 Scheduling policy 21
第三章、 系統設計與實作 26
3.1 量測系統架構 26
3.2 量測方法設計與實作 30
第四章、結果分析 37
第五章、結論與未來工作 45
5.1結論 45
5.2未來工作 45
參考文獻 46

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