I would like to start a dialogue and hear general feedback about the use of constraint triggers in postgres (8.4.5).
Our overall issue is that using general triggers is causing slow inserts (from locking issues) in our database. Here are some details:
A little background (jboss/j2ee/hibernate/linux)..... We have 3 basic triggers on a particular database table - one for inserts, one for updates & another for deletes and they keep track of a "granule count" that is used in reporting. This field (gracount) is stored in another table called dataset. An example of the insert trigger/function is as follows:
---------------------- CREATE TRIGGER increment_dataset_granule_count AFTER INSERT ON inventory FOR EACH ROW EXECUTE PROCEDURE increment_dataset_granule_count();
CREATE OR REPLACE FUNCTION increment_dataset_granule_count() RETURNS trigger AS $BODY$ DECLARE BEGIN IF NEW.visible_id != 5 THEN UPDATE dataset SET gracount = gracount + 1 WHERE dataset.inv_id = NEW.inv_id; END IF; RETURN NULL; END; $BODY$ LANGUAGE plpgsql VOLATILE COST 100; ALTER FUNCTION increment_dataset_granule_count() OWNER TO jboss; -----------------------
What we found was that when these triggers were fired we saw locking issues that slowed down performance dramatically to inserts into the inventory table (the table where the triggers are located). You could see the inserts sit and wait by looking at the pg_stat_activity table.
Within our app, the trigger was invoked within the same hibernate transaction that a stateless session bean was using to persist/merge the granule (inventory). Subsequently, in the same transaction, a EJB MBean was merging the dataset changes creating kind of a "dead lock" on the dataset table.
Our first try to solve this problem has been to convert these triggers into a constraint trigger which allows for DEFERRABLE INITIALLY DEFERRED flags. This, we are finding, is forcing the trigger function to run after the triggering transaction is completed. We believe this will fix our locking problem and hopefully speed up our inserts again.
Any comments or past experiences would certainly be helpful!
thanks,
Maria Wilson NASA/Langley Research Center Hampton, Virginia 23681
