Where is my database being updated?

I have recently added SaltedHashLoginGenerator into my code and can't
understand how my users table is being updated in response to a request
with the following parameters:

Parameters: {"user"=>{"id"=>"1"}, "action"=>"welcome",
"controller"=>"user",
"key"=>"62e047e834e688ebb215d1c5cc2bd1fca9fde33b"}

The action method "welcome" in the "user" controller is empty but Rails
seems to read the users row with id=1 and update a column within it
before invoking the Welcome action.

I'd be grateful for any pointers on how to find the trigger for this
behaviour.

btw, this is kind of a re-post of an earlier post but hopefully this is
clearer.