11.21. Signaling Events with Alerts (DBMS_ALERT)
The Oracle DBMS_ALERT package allows a process to post a message to another process and have that message delivered only after a commit. This is different from pipes where a process posts a message and that message will always be sent to the pipe, regardless of commit or rollback.
Pipe messages are sent immediately. Alerts are delivered only after the commit. A process can post many alerts. None can be received until the sending process has done a commit.
Alerts are asynchronous. The sender can send an alert signal whether or not a receiver has a posted read. This is also true with pipes. Receivers can post a read-wait with a timer or they issue a read and return. Senders and receivers communicate ...