PL/pgSQL graph enumeration function hangs

I have a table of organizations that has a many-to-many relationship
with itself via another table called relationships. The relationships
table has a serial id primary key and parent_id and child_id integer
fields. The organizations table has a couple thousand records and the
maximum depth is around 7 or 8 levels. The graph is directed and is (or
will be) reconvergent.

Using pseudocode from Celko's "SQL for Smarties" book, I wrote the
following function that builds a path enumeration table. I hope to
trigger this function on the rare occasions that the organizations table
is updated. But when I run this function, it hangs.

Can anyone spot the problem? If not, is there a better solution?

I am returning a trigger. There are no arguments. I'm using VOLATILE,
CALLED ON NULL INPUT, and SECURITY INVOKER.

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DECLARE
oldsize integer NOT NULL;
newsize integer NOT NULL;

BEGIN

-- recreate the empty path_enum table
DROP TABLE IF EXISTS organizations_path_enum;
CREATE TABLE organizations_path_enum (
parent_id integer NOT NULL,
child_id integer NOT NULL,
depth integer NOT NULL,
CONSTRAINT depth_not_negative CHECK( depth >= 0 )
);
CREATE INDEX ope_parent_idx ON organizations_path_enum(parent_id);
CREATE INDEX ope_child_idx ON organizations_path_enum(child_id);
CREATE INDEX ope_parent_child_idx ON
organizations_path_enum(parent_id, child_id);
CREATE INDEX ope_child_parent_idx ON
organizations_path_enum(child_id, parent_id);
CREATE UNIQUE INDEX ope_uniq_row_idx ON organizations_path_enum
(parent_id, child_id, depth);

-- load path of node to itself
INSERT INTO organizations_path_enum
SELECT DISTINCT child_id, child_id, 0 FROM relationships;

-- load paths of length = 1 into table
INSERT INTO organizations_path_enum
SELECT DISTINCT parent_id, child_id, 1 FROM relationships;

-- insert rows only while table grows
oldsize := 0;
SELECT COUNT(*) INTO newsize FROM organizations_path_enum;

WHILE oldsize < newsize LOOP
INSERT INTO organizations_path_enum
SELECT o1.parent_id, r1.child_id, (o1.depth + 1)
FROM organizations_path_enum o1, relationships r1
-- advance existing paths by one level
WHERE EXISTS (SELECT * FROM organizations_path_enum AS o2
WHERE r1.parent_id = o2.child_id)
-- insert only new rows into the table
AND NOT EXISTS (SELECT * FROM organizations_path_enum AS o3
WHERE o1.parent_id = o3.parent_id AND r1.child_id = o3.child_id);

oldsize := newsize;
SELECT COUNT(*) INTO newsize FROM organizations_path_enum;
END LOOP;
END;

-------------------------------------------------------------------------

Thanks!

Charles Munat
Seattle