DBMS_ALERT.WAITANY questions

I have somes questions about DBMS_ALERT package and WAITANY procedure.

The context is :
An application is waiting for database event (insert in a table). This application register a lot of signal identify by a special ID (about 1000 signals). This ID is a column of the waiting table. A trigger SIGNAL the ID when there is an insertion in the waiting table. The application use the WAITANY procedure to reveive events.

Problem is :
WAITANY don't return SIGNAL in a chronologic order. Questions are :
- In wich order the WAITANY procedure return raised SIGNALS ?

In the documentation, there is a chapter talking about POLLING LOOPS : If you use the WAITANY procedure, and if a signalling session does a signal but does not commit within one second of the signal.
- What is the inconvenient of POLLING LOOPS ?

• Should I use SET_DEFAULTS procedure ?
• I doesnt' understand how I can set up the POLLING LOOPS ? In the documentation there is two different sentences : The polling loop begins at a one second interval and exponentially backs off to 30-second intervals ? SET_DEFAULTS Sensitivity = Polling interval, in seconds, to sleep between polls. The default interval is five seconds ?