Explicitly dropping a database connection that is cached within a session context causes the session to be deleted. Session deletion in this manner is a cancel operation; any requests released from the session queue are in a canceled state. This action ensures that any outstanding requests waiting on the session are terminated. Similarly, a server or database shutdown cancels all database connections.
A session can be deleted by setting the SessionID option in the sa_set_http_option system procedure to null or an empty string.
The following code can be used for session deletion:
CALL sa_set_http_option( 'SessionID', null );
When an HTTP session is deleted or the SessionID is changed, any pending HTTP requests that are waiting on the session queue are released and allowed to run outside of a session context. The pending requests do not reuse the same database connection.
A session ID cannot be set to an existing session ID. Pending requests referring to the old SessionID are released to run as session-less requests when a SessionID has changed. Subsequent requests referring to the new SessionID reuse the same database connection instantiated by the old SessionID.
The following conditions are applied when deleting or changing an HTTP session:
The behavior differs depending on whether the current request had inherited a session whereby a database connection belonging to a session was acquired, or whether a session-less request had instantiated a new session. If the request began as session-less, then the act of creating or deleting a session occurs immediately. If the request has inherited a session, then a change in the session state, such as deleting the session or changing the SessionID, only occurs after the request terminates and its changes have been committed. The difference in behavior addresses processing anomalies that may occur if a client makes simultaneous requests using the same SessionID.
Changing a session to a SessionID of the current session (has no pending session) is not an error and has no substantial effect.
Changing a session to a SessionID in use by another HTTP request is an error.
Changing a session when a change is already pending results in the pending session being deleted and new pending session being created. The pending session is only activated once the request successfully terminates.
Changing a session with a pending session back to its original SessionID results in the pending session being deleted without any change to the current session.
Discuss this page in DocCommentXchange.
|Copyright © 2014, SAP AG or an SAP affiliate company. - SAP Sybase SQL Anywhere 16.0|