The schema for counters.py (https://gist.github.com/drsnyder/8222028).

counters.sql

CREATE TABLE counters (                                                                                                                                                                                                                       
  count_type INTEGER NOT NULL,
  count_id   INTEGER NOT NULL,
  count      INTEGER NOT NULL
);

-- later to fix the issue
ALTER TABLE counters ADD PRIMARY KEY (count_type, count_id);

CREATE TABLE primary_relation (
  id INTEGER PRIMARY KEY,
  a_counter INTEGER NOT NULL DEFAULT 0
);

INSERT INTO primary_relation
SELECT i FROM generate_series(1,5) AS i;

CREATE OR REPLACE FUNCTION increment_count(ctype integer, cid integer, i integer) RETURNS VOID
AS $$
BEGIN
    LOOP
        UPDATE counters
         SET count = count + i 
         WHERE count_type = ctype AND count_id = cid;
         IF FOUND THEN
            RETURN;
          END IF; 
        BEGIN
            INSERT INTO counters (count_type, count_id, count)
             VALUES (ctype, cid, i); 
            RETURN;
        EXCEPTION WHEN OTHERS THEN
        END;
    END LOOP;
END;
$$
LANGUAGE PLPGSQL;

CREATE OR REPLACE FUNCTION update_primary_a_count(ctype integer) RETURNS VOID
AS $$
  WITH deleted_counts_cte AS (
      DELETE
      FROM counters
      WHERE count_type = ctype
      RETURNING *
  ), rollup_cte AS (
      SELECT count_id, SUM(count) AS count
      FROM deleted_counts_cte
      GROUP BY count_id
      HAVING SUM(count) <> 0
  )
  UPDATE primary_relation
  SET a_counter = a_counter + rollup_cte.count
  FROM rollup_cte
  WHERE primary_relation.id = rollup_cte.count_id
$$ LANGUAGE SQL;