Title:	PERFORMANCE AND ADAPTABILITY OF REPLICATED WEB SERVICES THROUGH MESSAGE PACKING
Author(s):	Etienne Antoniutti Di Muro
ISBN:	972-99353-6-X
Editors:	Nuno Guimarães and Pedro Isaías
Year:	2005
Edition:	1
Keywords:	Web service replication, group communication, self-adaptation, message packing, performance improvement.
Type:	Full Paper
First Page:	31
Last Page:	40
Language:	English
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Paper Abstract:	As Web-based transactions become an essential element of everyday activities, it becomes increasingly important for Web application services scale adequately in the presence of wildly fluctuating input loads. Moreover, for today network-based service applications, dependability is a long-standing desirable property and replication has become a widespread way for enhancing dependability of Internet services. In this paper we are concerned with a replicated web service hosted by the Tomcat servlet container, where all replicas are kept strongly consistent based on a Group Communication system. Our focus is on improving the performance at service level by means of a Message Packing component interposed, in the middleware stack, between the replication machinery and the Group Communication layer. Message packing is a technique proposed earlier by Friedman and Van Renesse, in which multiple application-level messages are sent to all replicas through one single multicast. Our experiments show that this solution is effective in the context of a complete replicated application because it can significantly improve throughput and decrease CPU usage. A key feature of our approach is that the Message Packing component along with an Adaptation component companion is capable of fine tuning itself automatically and dynamically based on the specific load and operating environment. This adaptive behavior is obtained by means of a pluggable module that, at run-time through the readings of certain performance-related sensors, can modify the message packing parameters accordingly. Based on this architecture, different application-specific adaptation policies can be easily implemented.
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