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The session ID can be reset to another value by calling the sa_set_http_option system procedure with a new SessionID value. Changing the session ID has the effect of deleting the old session and creating a new session, but it reuses the current database connection so that state information is not lost. A SessionID can be set to NULL (or the empty string) which deletes the session. A SessionID cannot be set to an ID of an existing session (other than its own session ID in which case nothing happens). Trying to set a SessionID to an existing session's session ID will result in an "Invalid setting for HTTP option 'SessionID' SQLCODE=-939" error.
A server receiving a burst of multiple HTTP requests specifying the same session context queues (serializes) the requests on its session queue. In the event that the SessionID is changed or deleted by one (or more) of the requests, any pending requests in the session queue are requeued as individual HTTP requests. Each HTTP request will fail to obtain the session because it no longer exists. An HTTP request failing to obtain a session will default to sessionless operation and create a new database connection. The web application can verify that a request is operating within a session context by checking for a non-empty string value for the SessionID or SessionCreateTime connection properties. Of course, the web application can check the state of any application specific variables or temporary tables that it uses. Here is an example:
IF VAREXISTS( 'state' ) = 0 THEN // first invocation by this connection CREATE VARIABLE state LONG VARCHAR; END IF;