The high level topics covered in the book in depth are: Operating Systems, Java, Web Sphere Application Server, Web Servers and more.
At some point, represented by Section C, the buckle zone, one of the system components becomes exhausted. For example, the system might enter the buckle zone when the network connections at the web server exhaust the limits of the network adapter or if the requests exceed operating system limits for file handles.
Reducing the demand for resources can be accomplished in several ways.
Some critical sections of the application and server code require synchronization to prevent multiple threads from running this code simultaneously and leading to incorrect results.
Synchronization preserves correctness, but it can also reduce throughput when several threads must wait for one thread to exit the critical section.
In general, the goal of performance tuning is to increase throughput, reduce response times, and increase the capacity for concurrent requests, all balanced against costs. However, the response time increases proportionally to the user load.
For clustered configurations, check for uneven loading across cluster members.IBM Rational and other companies have tools to perform code profiling.An analysis of the application might reveal areas where some work might be reduced for some types of transactions.It is always important to consider what happens when some part of a cluster crashes. We recommend prioritizing work into short term (high), 3 months (medium) and long term (low).
How the work is prioritized depends on the business requirements and where the most pain is being felt.
When several threads are waiting to enter a critical section, a thread dump shows these threads waiting in the same procedure. If there is more traffic than the cluster can handle, will it queue and timeout gracefully?