8.4.2 Co-locating WebSphere applications
Each WebSphere application is different, and will have different requirements regarding heap size and overall process memory. If a customer's WebSphere applications after performance tuning and load testing do not require much memory to process efficiently, then performance gains may be seen by co-locating them on the same LPAR.
WebSphere Application Server runs as several processes, all executing the same Java runtime binary and probably under the same user ID (although this can be changed). A small, well-tuned and efficient low volume application might use 256-756 Mb of memory per process that should not be paged, and probably 50-250 threads, maybe more. This means that an efficient low-volume Web application might need less than 25% of a processor, and as little as 128 Mb memory. Managing such requirements are well within the AIX workload management scope.
These processes may run independent applications funded by different businesses. Some applications may need more than one process (JVM) to achieve the desired capacity, in which case they will be cloned JVMs. Clones form a group, called a cluster. All processes in a cluster have the same configuration and run the same application. There is also an administrative process (actually another process just like the others, but running a different application) performing shared services for the other processes under its administration. The SLA and the resource plans are at the application level, so we need to manage the application as the aggregation of these JVM processes.
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