During transmit (Write it out in Java to the log file) but if you just want it in the Agentry client you can try a few ways:
1) Create a screen (Detail screen with some labels) to be only enabled when you hit a certain number of records and to display that screen. It gets disabled (unseen) when you do not hit a certain mark.
2) If you are dealing with a transaction with screen, you may have a validation rule that will notify the user (warning) that they have a complex table that is X big.
But the screen is the easiest one as you just create an enable rule to turn on the screen in one of your favorite screenset.
Hope this helps gives some ideas. Some other consultants may do it differently.
SAP Platinum Support Engineer