most simply implementation of history table with hstore extension

Postgres has this nice extension (hstore) lot of years. It can be used for simulation some features of doc databases - or can be used for implementation of generic triggers for history table:

I have a table test and table history:

CREATE TABLE test(a int, b int, c int);

CREATE TABLE history(
  event_time timestamp(2),
  executed_by text, 
  origin_value hstore, 
  new_value hstore
);

CREATE OR REPLACE FUNCTION history_insert()
RETURNS TRIGGER AS $$
BEGIN
  INSERT INTO history(event_time, executed_by, new_value)
     VALUES(CURRENT_TIMESTAMP, SESSION_USER, hstore(NEW));
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION history_delete()
RETURNS TRIGGER AS $$
BEGIN
  INSERT INTO history(event_time, executed_by, origin_value)
     VALUES(CURRENT_TIMESTAMP, SESSION_USER, hstore(OLD));
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION history_update()
RETURNS TRIGGER AS $$
DECLARE
  hs_new hstore := hstore(NEW);
  hs_old hstore := hstore(OLD);
BEGIN
  INSERT INTO history(event_time, executed_by, origin_value, new_value)
     VALUES(CURRENT_TIMESTAMP, SESSION_USER, hs_old - hs_new, hs_new - hs_old);
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER test_history_insert AFTER INSERT ON test
  FOR EACH ROW EXECUTE PROCEDURE history_insert();

CREATE TRIGGER test_history_delete AFTER DELETE ON test
  FOR EACH ROW EXECUTE PROCEDURE history_delete();

CREATE TRIGGER test_history_update AFTER UPDATE ON test
  FOR EACH ROW EXECUTE PROCEDURE history_update();

Result:

INSERT INTO test VALUES(1000, 1001, 1002);
UPDATE test SET a = 10, c = 20;
DELETE FROM test;

postgres=# SELECT * FROM history ;
       event_time       | executed_by |           origin_value            |               new_value               
------------------------+-------------+-----------------------------------+---------------------------------------
 2015-01-15 20:59:05.52 | pavel       |                                   | "a"=>"1000", "b"=>"1001", "c"=>"1002"
 2015-01-15 20:59:05.6  | pavel       | "a"=>"1000", "c"=>"1002"          | "a"=>"10", "c"=>"20"
 2015-01-15 20:59:06.51 | pavel       | "a"=>"10", "b"=>"1001", "c"=>"20" | 
(3 rows)

Tested on PostgreSQL 9.2