Scheduled invalidation

Instead of relying on the periodic invalidation timer that runs on an interval based on the session timeout parameter, we can set specific times for the session management facility to scan for invalidated sessions in a distributed environment.

When used with distributed sessions, this feature has the following benefits:

• We can schedule the scan for invalidated sessions for times of low application server activity, avoiding contention between invalidation scans of database or another WebSphere Application Server instance and read and write operations to service HTTP session requests.

• Significantly fewer external write operations can occur when running with the End of Service Method Write mode because the last access time of the session does not need to be written out on each HTTP request. (Manual Update options and Time Based Write options already minimize the writing of the last access time.)

• The session manager invalidates sessions only at the scheduled time, therefore sessions are available to an application if they are requested prior to the session is invalidated.

Usage considerations:

• With scheduled invalidation configured, HttpSession timeouts are not strictly enforced. Instead, all invalidation processing is handled at the configured invalidation times.

• HttpSessionBindingListener processing is handled at the configured invalidation times unless the HttpSession.invalidate method is explicitly called.

• The HttpSession.invalidate method immediately invalidates the session from both the session cache and the external store.

• The periodic invalidation thread still runs with scheduled invalidation. If the current hour of the day does not match one of the configured hours, sessions that have exceeded the invalidation interval are removed from cache, but not from the external store. Another request for that session results in returning that session back into the cache.

• When the periodic invalidation thread runs during one of the configured hours, all sessions that have exceeded the invalidation interval are invalidated by removal from both the cache and the external store.

• The periodic invalidation thread can run more than once during an hour and does not necessarily run exactly at the top of the hour.

• If we specify the interval for the periodic invalidation thread using the HttpSessionReaperPollInterval custom property, do not specify a value of more than 3600 seconds (1 hour) to ensure that invalidation processing happens at least once during each hour.

Session management tuning