Query using partitioned table hangs

A re-post, since I'm really stuck on this and could use some advice on how to troubleshoot this...

I have an app that was previously using a large unpartitioned table with no problems. I partitioned this table and am now experiencing intermittent hangs when inserting data into the partitioned table. The stored procedure that does the insert seems to run to completion even when it 'hangs'. There are no messages in the log file, no errors/exceptions that I'm aware of, and I'm at a loss as to what is causing this, so any help would be much appreciated.

Here's the details:

PostgreSQL version: 8.4
OS: Reproduced on both, RHEL 5.3 and OS X 10.5
Application: Java 1.6, using PostgreSQL 8.4 JDBC type 4 driver.

The application invokes a pl/pgsql stored procedure (with autocommit set to true). This sproc does several inserts - see below for the code. This works fine with a single unpartitioned table, even for large inserts.

With the table partitioned, it hangs intermittently, usually occurs within 20 - 30 minutes of running the application, after invoking the sproc ~25 times. When it hangs, it hangs indefinitely - I know because I inadvertently left it in 'hung' state for 24 hours, so it's not just slow.

The last command of the sproc truncates the staging table, raw_data. The table raw_data is empty when the query is hung, which suggests that the sproc is running to completion. I tried sending a SIGHUP to the postmaster process (kill -1) while the sproc was hung, thinking it might be a thread blocked somewhere, but that had no effect.

The relevant tables, queries etc are listed below:

-- The parent table
CREATE TABLE event (
id BIGSERIAL PRIMARY KEY,
evt_time TIMESTAMP WITH TIME ZONE NOT NULL,
fk_host INTEGER REFERENCES dim_host NOT NULL,
fk_user INTEGER REFERENCES dim_user
);

-- example of a child table:
CREATE TABLE event_y2009m09
(
CONSTRAINT event_y2009m09_evt_time_check CHECK (evt_time >= '2009-09-01'::date AND evt_time < '2009-10-01'::date)
)
INHERITS (event)
WITH (
OIDS=FALSE
);

-- Example of trigger function used
CREATE OR REPLACE FUNCTION event_insert_trigger()
RETURNS trigger AS
$BODY$
BEGIN
IF ( NEW.evt_time >= DATE '2009-08-01' AND NEW.evt_time < DATE '2009-09-01' ) THEN
INSERT INTO event_y2009m08 VALUES (NEW.*);
ELSIF ( NEW.evt_time >= DATE '2009-09-01' AND NEW.evt_time < DATE '2009-10-01' ) THEN
INSERT INTO event_y2009m09 VALUES (NEW.*);
ELSE
RAISE EXCEPTION 'Date out of range.';
END IF;
RETURN NULL;
END;
$$
LANGUAGE plpgsql;

-- The sproc that hangs
CREATE OR REPLACE FUNCTION normalize_data()
RETURNS void AS
$BODY$
DECLARE
str_value text;
match record;
BEGIN
-- Run analyze to keep statistics up to date
-- raw_data contains ~60,000 records at this point
ANALYZE raw_data;

INSERT INTO dim_host (name_str)
SELECT DISTINCT host_name FROM raw_data
EXCEPT
SELECT name_str FROM dim_host;
ANALYZE dim_host;

-- Do a few more inserts like the above

-- Then copy all the records from the staging table
-- Simplified for brevity - real query is a 12-way join
-- All FK constraints on table event are dropped before
-- we run this query.
-- All appropriate partitions and triggers have been created
-- in advance of running this query.

INSERT INTO event (evt_time, fk_host, fk_user)
SELECT r.evt_time, dim_host.id, dim_user.id
FROM raw_data as r
JOIN dim_host ON r.host_name = dim_host.name_str
LEFT JOIN dim_user ON r.user_name = dim_user.user_name;

TRUNCATE raw_data;

RETURN;
END;
$$ LANGUAGE plpgsql;