Transaction commit in a trigger function

Hi there,

I'm using PG 8.2.3.

Is it possible to (somehow) commit a specific statement in a trigger
function if the function itself is rolled back because of an error (eg, for a
unique index error)?

For example:

create table tab1 (col1 int unique);
create table tab2 (col1 int);

CREATE OR REPLACE FUNCTION
f_func1 () RETURNS trigger AS $$
BEGIN
-- ... some processing ...

INSERT INTO tab2 (col1) VALUES (new.col1);
-- COMMIT the above statement, irrespective of whether this
-- trigger/function is rolled back or not.

RETURN new;
end;
$$ LANGUAGE 'plpgsql';

CREATE TRIGGER tiu_t1
BEFORE UPDATE OR INSERT ON tab1
FOR EACH ROW
EXECUTE PROCEDURE f_func1();

* * *

Now, if you:

insert into tab1 (col1) values (1);

and tab1 already has a row with col1=1, tab2 must be updated even when
the statement fails with:

ERROR: duplicate key violates unique constraint...

I know this can be achieved outside the DB (ie, with checks, etc), but I'd
like to keep this aspect inside the DB. Also, I could perform selects inside
the trigger to pre-empt a unique constraint error, but this will slow the
inserts down.

I can't wrap BEGIN/COMMIT around the INSERT in the trigger. Is there
another way of achieving this?

Any suggestions are appreciated.

Regards