Quality of Service Controls in Web Servers

January 16, 2007 -- TRLabs has developed a novel service differentiation policy that allows for a server to guarantee a certain Quality of Service (QoS).

Benefits…

 • Easily deployable
• Allows the operator a great amount of control.
• Server can allocate resources according to QoS requirements of different classes of web-traffic.
Background
Amidst growing competition, web service providers are increasingly becoming interested to better serve their clients. The traditional approach of a best-effort single class service policy in web servers is proving inadequate because of several reasons. First, the diverse set of competing services provided by web servers have different performance requirements. Second, the requests for the web content compete for the limited resources in the web servers to get serviced. Moreover, in shared hosting facilities, different business and corporate organizations pay for hosting their web contents and expect performances according to the amount they pay to arrange services for their clients. The client satisfaction or expectations are often abstracted in the Quality of Service (QoS) they receive and thus, the web server has to be QoS aware. Such a QoS-aware web server adopts differentiated service policy to make sure that the clients are serviced according to their expectations and the importance of the service requests. The service providers are often willing to guarantee that certain services or certain clients get a predefined amount of performance from the server, while maintaining a best-effort approach for the rest. The differentiated service policy has to be designed to meet this requirement. In addition to meeting the guarantees, the service providers often look for reaching certain optimization objectives.

One simple and straightforward approach for deploying differentiated service is to adopt priority queuing schemes in the web server. A number of research works have demonstrated that prioritized scheduling of requests in web servers according to their service requirements can give performance benefits to some premium (high priority) class of requests over some non-premium (low priority) requests. The advantage of priority based schemes is that they are simple to implement and offer ease of integration into the existing web servers. However, the strict priority based schemes fail to offer the desired service differentiation when the service providers need to control the allocation of web server resources to meet QoS guarantees. It offers the differentiation without the means to control the differentiation, whereas the service providers need some "control knob" in their hands. Many admission control and scheduling algorithms have been proposed in the literature to offer this control knob to the service providers. However, they lack the simplicity and ease of integration enjoyed by priority based schemes.

TRLabs has developed an analytic approach to obtain a controllable service differentiation policy based on the concept of dynamic priority queuing. The approach used was free from the drawbacks of strict priority based schemes. It can offer the service provider the necessary control on resource allocation for meeting QoS guarantees and for meeting the desired service differentiation objectives. It also obviates the adoption of complex admission control and scheduling schemes and retains the advantages of simplicity and the ease of implementation of priority based schemes.
Project Status
TRLabs has developed a service differentiation policy based on the concept of dynamic priority queuing. This policy was demonstrated in a practical scenario by conducting a real web trace. From the numerical results and analysis, it was found that by adopting this method, service providers can obtain a service differentiation policy with tunable control parameters, which can be set to appropriate values to ensure QoS guarantees and to reach desired service differentiation objectives.

Research Supervisors
M. (Mahes) Maheswaran t: 514.398.1465 e:
Ekram Hossain t: 204.474.8908 e:

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