WebSphere Application Server V8.5 Administration and Configuration Guide for the Full Profile

506 WebSphere Application Server V8.5 Administration and Configuration Guide for the Full Profile

Session affinity

Session affinity means that all requests of the same JSESSIONID are sent to the same

application server, regardless of the LoadBalanceWeight.

When using round robin for the LoadBalance option, the following options are available to

handle affinity requests:

 Configure the parameter IgnoreAffinityRequests to true. The affinity requests do not lower

the weight. This behavior might cause an uneven distribution of requests across the

servers in environments that make use of session affinity.

 Configure the IgnoreAffinityRequests to false. The weight is lowered by each affinity

request, leading to a more balanced round robin environment.

Fail-over

Fail-over occurs when the plug-in marks an application server (or clone) as down and then

sends the pending requests to another member of the same cluster. This can happen if the

plug-in is unable to open a new connection to the appserver within the ConnectTimeout. Or

fail-over can happen if the plug-in already sent the request to the application server but does

not receive a response from the application within ServerIOTimeout.

While an application server is marked as down, the plug-in no longer sends any requests to it

until the interval defined in the RetryInterval parameter is met. After that, the plug-in checks to

see if that application server can be used successfully again, removing the "down" flag if a

positive response is received.

For more information about plug-in tuning and configuration, refer to the following website:

http://www-01.ibm.com/support/docview.wss?uid=swg27021301

To understand how load balancing works in the Web server plug-in, see Understanding IBM

HTTP Server plug-in Load Balancing in a clustered environment, at the following website:

http://www-01.ibm.com/support/docview.wss?uid=swg21219567

To understand how fail-over works in the Web server plug-in, see Understanding HTTP

plug-in failover in a clustered environment, at the following website:

http://www-01.ibm.com/support/docview.wss?uid=swg21219808

14.3 JVM tuning

In this section, we provide information about the JVM parameters that you can tune to

increase system performance. You can set the majority of parameters that we explain in this

section from the administrative console. Complete the following steps:

1. Navigate to Servers  Application servers  <AppServer_Name>.

2. Under System Infrastructure, expand Java and Process Management  Process

definition  Java Virtual Machine.

3. Use the Configuration window to specify the JVM settings.

4. Click Apply.

For detailed information about the concepts that we explore in this section, refer to the Java

Diagnostics Guide at the following website:

http://publib.boulder.ibm.com/infocenter/javasdk/v6r0/topic/com.ibm.java.doc.diagn

ostics.60/homepage/plugin-homepage-java6.html