10.11.1 Session size

Large session objects pose several problems for a Web application. If the site uses session caching, large sessions reduce the memory available in the WebSphere instance for other tasks, such as application execution.

For example, assume a given application stores 1 MB of information for each user session object. If 100 users arrive over the course of 30 minutes, and assume the session timeout remains at 30 minutes, the appserver instance must allocate 100 MB just to accommodate the newly arrived users in the session cache:

1 MB for each user session * 100 users = 100 MB

Note this number does not include previously allocated sessions that have not timed out yet. The memory required by the session cache could be considerably higher than 100 MB.

Web developers and administrators have several options for improving the performance of session management:

Reduce the size of the session object.

Reduce the size of the session cache.

Add additional appservers.

Invalidate unneeded sessions.

Increase the memory available.

Reduce the session timeout interval.