transport_maps and lookups reason


I have 'transport_maps = mysql:/etc/postfix/' in
configuration and want to understand the reason of every db lookup as I
have some actions in mysql server based on queries count. Please explain

When sending single email these lookups are made:

1. "*"
2. "source@emal"
3. "destination@email"
4. "destination@email"

Especially what directives cause lookups over "mail from" address and
why destination address is called twice?

I have single mysql inclusion in configuration.

postfix 3.3.0