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