PostgreSQL intenal scheduler?

Hi all

I am designing a framework for historisation implementation (SCD). One  
feature I would like to provide is a table in that the actual state of  
an entity is put and if this is complete, this history table is  
"updated":

       ------------         -------------
==>  | ENTITY_ACT |  ==>  | ENTITY_HIST |
       ------------         -------------

I plan to use instead-of-triggers on the hist table that read the  
actual table and perfoms all necessary inserts und updates on the  
history table. If I want the termination of a record version (actually  
the record of a specific business key with a specific payload) to get  
propagated up and/or down referential integrities (no overlapping  
validities) I have to make sure that only one of those processes is  
modifying a table. I was thinking of a scheduler queue where the  
trigger would put a process request and PostgreSQL would work through.  
Is there a scheduler within PostgreSQL? I read the documentation and  
searched the web but could not find a hint. But before going another  
road or implementing something myself, I ask. Maybe this design is no  
good at all.

Kind regards

Thiemo