IBM BS029ML Self Help Guide - Page 46
WebSphere queuing mechanism, WebSphere Application Server embedded Web Container
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Tip: Our experience has shown that many customers fail to implement vertical clustering when horizontal clustering is implemented to address the needs of high availability. As such, it is an IBM recommended best practice that both vertical and horizontal clustering are implemented to address the needs of scalability, high availability, and operational availability. 2.5.3 WebSphere queuing mechanism In order to understand how to maximize performance, it is necessary to understand the WebSphere queuing mechanism. WebSphere implements a componentized architecture, channeling requests through a number of queues. These queues or pools include a Proxy server and Web server (considered even though they are external components), the WebSphere Application Server embedded Web Container, the EJB™ container, data sources, and possibly other connection pooling mechanisms to various custom back-end systems. Each of these resources sustains a queue of requests waiting to use the resource in question. The overall queuing mechanism is designed to converge towards the back end, where resources are deemed more expensive. For example, out front it is not uncommon for the Web server queue to be configured to handle an inordinately large number of requests. This contrasts to a data source pool, which by nature is more expensive (both in terms of CPU and memory) and thus usually only configured to handle a maximum of 10-20 connections simultaneously. Each queue has the potential to become saturated. There also exists the possibility that if one of the back-end queues saturates, that it will have an effect on the other queues in front. For example, it is not unusual that if a data source connection pool saturates, that the Web container will also eventually overload (simply due to the fact that requests cannot be processed further downstream). This can be particularly confusing when investigating performance. In which case, it is recommended that you take a holistic approach to performance tuning and determine which queue saturates first. Web Server Web Container EJB Container Data Source Figure 2-4 WebSphere queuing mechanism 32 IBM WebSphere Portal V6 Self Help Guide
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