Oracle Database Discussions

As a DBA, I sometimes kill sessions from within SQL*Plus by entering command "ALTER SYSTEM KILL SESSION 'xxx,xxxx';". Sometimes the session ends quickly, sometimes it takes minutes for the killed session to go away.

When I use Enterprise Manager Grid Control to kill a session I must choose between a "Kill Immediate" or "Post Transactional". When I kill a session by entering a command from within SQL*Plus I do not use either of these options.

I am trying to understand the consequences of using the two options offered via grid control. Some forum postings suggest you use the IMMEDIATE" clause only as a last resort. They say it could prevent a session from completeing a rollback of updates since the operating system process is terminated immediately. Reading a description of the POST_TRANSACTION clause makes me think issueing the command against a long running query will allow it to continue running and terminate the session only after the SQL query ends. For now I avoid using either of the grid control options and stick with my original format in SQL*Plus.

Could someone shed light on the difference between killing a session with or without the KILL IMMEDIATE or POST_TRANSACTIONAL" options?

Thank you,
Bill