网络QoS机制不足以提供完全的端到端的性能保证,在由三层结构构成的电子商务网站中,基于反馈控制理论,提出并实现了在应用服务器的数据库连接池中的绝对延迟保证,对数据库连接池作出了改进,确保带有高优先级请求的平均排队延迟不超过设定的阈值.通过系统辨识建立了数据库连接池的近似线性时不变模型(LTI),并设计了绝对延迟保证控制器,为Tomcat Web应用服务器实现了数据库连接池中闭环系统所有部件.测试结果表明,即使在并发请求数量剧烈变化时,控制器的设计也是有效的.%Network QoS mechanisms are insufficient to provide complete end to end performance guarantees. In e-commeree Web sites composed of a three-tiered architecture, this paper proposed and implemented absolute delay guarantee in the database connection pool(DBCP)in Web application servers based on feedback control. It improved the database connection pool to ensure that the response time for requests with high priority was no more than the threshold specified. It set up the approximate linear time-invariant models of the DBCP through system identification and designed the absolute delay guarantee controller. It implemented all the components of closed-loops in a real DBCP for the Tomcat Web application server. Test results show that the controllers designing is effectively even if the number of concurrent requests varies severely.
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