You might have stuff running in a few different worksheets and editors. The button will activate once something’s running in the worksheet. Hitting this button will send the cancel request to the database. So let’s get back to the actual query being cancelled. That’s kind of out-of-scope for this post, but I’m going to say it’s out of the client’s (SQL Developer’s) hands.
PMON is responsible for doing the clean-up there. Or maybe the client sees the query as cancelled but you still see the server process (PID) running on the server. It’s the ‘maybe’ part that frustrates people. Maybe the database hears you and maybe it cancels the query. We let the database know you changed your mind. A few moments later, you change your mind and hit the ‘Cancel’ button. This reminds me of the weather forecasting models can that could be perfect but would take years to run…anyway I’m digressing way too early already. Maybe that data you asked for wasn’t going to be that helpful if it took 3 hours for it to come back. It’s like that one time you posted that picture on Facebook and immediately (3 days later) you realized it wasn’t a great career move.
I’m not sure why, but it appears many of you wish you could take back your SQL queries.
