e-Marketplace Pattern using WebSphere Commerce Suite, MarketPlace Edition Patterns for e-business Series

64 e-Marketplace Pattern using WebSphere Commerce Suite, Marketplace Edition

5.4.9 Web server stay alive

These directives deal with the persistent connection feature of the HTTP V1.1

specification. With HTTP V1.0, each HTTP session establishes a new TCP

connection. If your home page has a lot of images, you will need to establish

TCP connections many times to send all data for one page. The persistent

connection feature is designed to avoid this behavior. After one session is

finished, the connection still remains and the next request can re-use the

connection. If IHS gets an HTTP/1.1 request, IHS can re-use the connection

until it receives the connection close request. The directives to understand

are:

• KeepAlive - Whether or not to allow persistent connections (more than one

request per connection). Set to "off" to deactivate. The default is on.

• KeepAliveTimeout - Number of seconds to wait for the next request. The

default value is 15. To avoid waiting too long for the next request, you can

specify the number of seconds to wait. Once the request has been

received, the Timeout directive will apply.

• MaxKeepAliveRequests - The maximum number of requests to allow

during a persistent connection. Set to 0 to allow an unlimited number.

• Timeout - Sets the number of seconds the IHS waits for these three

events:

- Time taken to receive a GET request.

- Time taken between receipt of TCP packets on a POST or PUT

request.

- Time taken between acknowledgments on transmissions of TCP

packets in responses. The default value is 300.

5.5 Application server

For an application server in WebSphere V3 there are a number of settings

that have an impact on performance. In addition to the settings for the

application server itself there are also a number of settings for the various

components of an application server; servlet engine, Web application, and

the EJB container, that can affect performance. The following parameters are

set using the WebSphere Application Server Administrative Console:

• Java Virtual Machine (JVM)

• Threads

These parameters will be discussed in detail in the following sections.

Chapter 5. Performance guidelines 65

5.5.1 Selecting a JVM

High-performance JVMs are critical for good performance. Here are some

considerations when evaluating JVMs:

1. Java compiler and virtual machine technology changes rapidly. Today a

JIT version of a compiler may provide the best performance for your

solution; Tomorrow it may be a static compiler, and next week there may

be a new technique.

2. A JVM should be certified for portability by a recognized certification

authority such as JavaSoft.

3. JVMs that have been optimized for a specific operating system tend to

perform better than other JVMs.

4. Systems with symmetric multiprocessors (SMP) tend to perform better

because of the thread support in Java. Use JVMs that effectively support

SMP systems.

5. Evaluate the trade-off between the stability of the current release of a JVM

and the performance enhancements available in the newest beta release

and/or production version.

Generally speaking, the selection of a JVM should be of little concern to you.

The performance of applications can often be better improved by improving

the runtime characteristics of the algorithms used. However, there are

circumstances, such as computationally intensive programs, where an

improvement in the performance of the underlying JVM will add to the

solution’s overall performance.

5.5.2 Threads

Each application server has its own thread pool from which it uses threads to

process remote method invocations. This pool size varies throughout the

servers lifetime. Threads are created when needed and destroyed when there

are too many idle threads. Each application server has a setting for thread

pool size. Consider increasing the thread pool size if analysis shows that the

maximum number of threads in the pool are frequently in use.

5.5.3 Caching

The addition of memory to a system almost always improves performance.

This is because physical I/O is a relatively expensive operation in terms of

latency. It makes intuitive sense that by, dedicating memory in a Web server

to store frequently accessed HTML pages and images, you will improve

performance. As a rule of thumb, your Web server should have enough RAM

to accommodate all network buffers, frequently used applications, images