228 A Portal Composite Pattern Using WebSphere Portal V5
way to disable the parallel mode is to use the -Xgcthreads parameter to change
the number of garbage collection helper threads being started.
When using concurrent mode, a background thread is started by the JVM
(independently from the garbage collection helper threads), and some part of the
work is done in the background while the application threads are active. The
background thread tries to complete part of the garbage collection work
concurrently with the application, so that when garbage collection does kick in,
the resulting STW pause will be reduced.
In some cases, though, concurrent processing can have a negative impact on
performance, especially for CPU-intensive applications.
Use the -verbosegc command line parameter to track your garbage collection
operations. Enabling verbosegc can have a performance impact on an
application. If such impact is unacceptable, a test system should be used to
collect the verbosegc logs. It is common for server applications to keep
verbosegc enabled at all times. This can be a good way to monitor the overall
health of the JVM, and can be invaluable in post-mortem if an OutOfMemory
error occurs.
For more information on garbage collection, see:
򐂰 WebSphere Application Server InfoCenter
򐂰 “Fine-tuning Java garbage collection performance,” by Sumit Chawla,
Technical Lead, eServer Java Enablement, IBM
8.8 Performance guidelines
In this section we present a conceptual overview on caching and object pooling
strategies. Both can help you to build scalable and well-performing portlet
applications. In addition, we point out some common performance pitfalls in
portlet coding.
8.8.1 Caching
Caching is a vital part of any Web application when you are trying to optimize
performance, but caching can also be very difficult to implement.
Chapter 8. Portal application design and development guidelines 229
As a solution and application designer, you should consider the caching
possibilities as early as possible in your designs. There are two important forms
of caching.
Product-delivered caching
The standard products that are typically used in Web applications often offer
different caching mechanisms that can be used. It is important to understand
which products in the operational model offer caching, and how they can be
򐂰 HTTP servers
HTTP servers typically offer caching of static content, like images, static html
files, javascript, and css files. It is generally a good idea to have the HTTP
server serve these items instead of the application server. For more
information on IBM HTTP Server caching, see:
򐂰 Application servers
Application servers like WebSphere Application Server have servlet caching
for caching content delivered by the Web applications running at the server.
They also deliver prepared statement caching for optimizing access towards
the used database. For more information on WebSphere Application Server
򐂰 Portal server
WebSphere Portal has different cache settings, which you can tune in order to
gain performance improvements. These cache settings are stored in property
files in the WP_ROOT/shared/app/config/ directory.
There are no particular settings to gain the most performance; instead, the
settings have to be in sync with the non-functional requirements of your
As an example, you should consider how long your unpersonalized pages are
to be cached. By default, WebSphere Portal only caches them for 60
seconds. If you are not creating, updating, or deleting pages several times an
hour on your production system, you might want to consider increasing this
setting. On the other hand, you do not want to wait hours to see a change
take effect.
Another example is the caching of the users access rights. Often the user’s
access rights are based on the group of which he is a member. Consider the
time that access rights are to be cached, based on the relative stability or
volatility of your access group memberships and individual access rights

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