IBM WebSphere changed parameters in the JDK in IBM JDK1.4.2 SR3. Any WebSphere version using IBM JDK 1.4.2 SR3 or greater is affected.
The change may cause WebSphere to hold onto unused objects for up to ten minutes after they are no longer needed. In high usage environments, this may act as a memory leak so that the application is starved for memory. There is a parameter to control this behavior, ackTimeout.
Some networks may also benefit from a parameter change in the JDK to set the default TCP/IP stack to V4. This can improve network performance by since the default behavior will be for the standard IP V4 and WebSphere will not need to determine the IP type programmatically. This parameter is -Djava.net.preferIPv4Stack.