Immutable table functions

Hello guys,

I don't know if this is the correct list. Correct me if I'm wrong.

I have a directed graph, or better, a tree in postgresql 8.3. One table are
the nodes and another one are the connections. Given any node, I need to get
all nodes down to it(to the leafs) that have relation with anotherTable.
Also, this connection change on time, so I have a connectionDate and a
disconnectionDate for each connection (which might be null to represent open
interval). This way, I wrote a pgsql function (I rename the tables and
columns to generic names). These are the tables and the function:

CREATE TABLE node (

id_node integer NOT NULL,

CONSTRAINT node_pkey PRIMARY KEY (id_node)

);

CREATE TABLE anotherTable

(

id_anotherTable integer NOT NULL,

id_node integer NOT NULL,

CONSTRAINT anothertable_pkey PRIMARY KEY (id_anotherTable),

CONSTRAINT anothertable_node_fkey FOREIGN KEY (id_node) REFERENCES node.
id_node

MATCH SIMPLE ON UPDATE NO ACTION ON DELETE NO ACTION

);

CREATE TABLE connection

(

id_connection integer NOT NULL,

down integer NOT NULL,

up integer NOT NULL,

connectionDate timestamp with time zone,

disconnectionDate timestamp with time zone,

CONSTRAINT connection_pkey PRIMARY KEY (id_connection),

CONSTRAINT down_fkey FOREIGN KEY (down)

REFERENCES (id_node) REFERENCES node. id_node MATCH SIMPLE

ON UPDATE NO ACTION ON DELETE NO ACTION,

CONSTRAINT up_fkey FOREIGN KEY (up)

REFERENCES (id_node) REFERENCES node. id_node MATCH SIMPLE

ON UPDATE NO ACTION ON DELETE NO ACTION);

CREATE TABLE observation

(

id_observation integer NOT NULL,

id_node integer NOT NULL,

date timestamp with time zone,

CONSTRAINT observation_pkey PRIMARY KEY (id_observation),

CONSTRAINT observation_node_fkey FOREIGN KEY (id_node) REFERENCES node.
id_node

MATCH SIMPLE ON UPDATE NO ACTION ON DELETE NO ACTION

);

CREATE OR REPLACE FUNCTION
get_nodes_related_to_anothertable(integer,timestamp with time zone) RETURNS
SETOF integer AS 'DECLARE
_id ALIAS FOR $1;
_date ALIAS FOR $2;
_conn RECORD;
BEGIN
return query SELECT 1 FROM anothertable WHERE id_node = _id;
FOR _ conn IN SELECT * FROM connection c where c.up = _id LOOP
if _conn. connectionDate > _date then
continue;
end if;
if _conn. disconnectionDate < _data then
continue;
end if;
return query SELECT * from
get_nodes_related_to_anothertable(_conn.down, _date);
END LOOP;
END' LANGUAGE 'plpgsql' IMMUTABLE;

And I use it on my SELECT:

SELECT

*

FROM

(SELECT

id_node,

date

FROM

observation

) root_node_obs,

node,

anotherTable

WHERE

anotherTable.id_node = node.id_node

AND

node.id_node IN (

select * from get_nodes_related_to_anothertable(root_node_obs
.id_node,root_node_obs .date));

Even with IMMUTABLE on the function, postgresql executes the function many
times with the same parameters. In a single run:

select * from get_nodes_related_to_anothertable(236,now());

it returns 5 rows and runs in 27ms. But in the bigger SELECT, it take 5s to
each observation row (and I may have some :-) ).

I know that IN generally is not optimization-friendly but I don't know how
to use my function without it.

Any clues guys?

Thanks,