What are the differences between WWW sessions and sessions in other services?
Two pages in the GMS administration interface refer to sessions, Security->Sessions and Incoming->Threads. The values for WWW are very different between the two locations, so what is meant by "Sessions" in each case?
In the case of SMTP, POP and POST, threads and sessions are actually the same thing, any connection in one of these services uses a thread and creates a session at the same time. When the transaction ends, the session is destroyed and the thread released.
In the case of WWW and IMAP, when a client connects, a thread is used to create a session, and perform an action. So in WWW the thread would be used to display the initial logon page and create a session. This would take a fraction of a second, and so the thread is only used for a short time.
The session however will exist for as long as the timeout period (Security->Connections) for that interface, even if the user does nothing, or closes the browser. When the user logs on, a number of actions occur each of which will use a thread for a short time. The session will persist throughout this period.
If a user closes the browser, the session will exist for the timeout period then be destroyed. If the user logs off or has a timed log off, the session will be terminated.
Furthermore, if any scripts are being used (such as the filters in GMS Webmail and the Anti-Spam filters) any time these are run the SMTP service passes the message to the WWW service, and a session will be created for the script to be processed, when processing is complete the session is terminated.
This means that a much higher number of sessions can be supported by a lower number of threads. The default setting of 32 WWW threads is used in conjunction with a setting of 1000 WWW sessions.