Here is a scenario:

DBSinkPE- writes the event to the database.
DBKeySelector- based on the event id picks which db to write to.

The problem is simple sharding by using modulus. In the PE I need to know which key the event belongs to so I can create the right jdbc url.

#1 I can call the KeyFinder again... seems clunky.
#2 I can mark the event with the Key in the KeyFinder... probably works.

#3 some elegant method you will tell me...