Postgres Function not working when I have a large result - sql

Question

I'm copying information from table 1(tmp_subtype) to table 2(subtype_user). I have a test table 1 with 15 registers. I run this function into postgres:
CREATE OR REPLACE FUNCTION VERIFY_AND_INSERT_SUPTYPE()
RETURNS text AS $$
DECLARE
register_subtype RECORD;
existe INT DEFAULT 0;
MESSAGE_EXCEPTION TEXT;
cursor_subtype CURSOR
FOR
SELECT tsd.subtype,tsd.type_id_client,tsd.id_client,tsd.email
FROM tmp_subtype tsd;
BEGIN
OPEN cursor_subtype;
LOOP
FETCH cursor_subtype INTO register_subtype;
EXIT WHEN NOT FOUND;
SELECT COUNT(*) INTO existe FROM (
SELECT sdu.id_client FROM subtype_user sdu
WHERE sdu.id_client = register_subtype.id_client AND sdu.type_id_client = register_subtype.type_id_client
LIMIT 1
) SUB0;
IF existe = 0 THEN
INSERT INTO subtype_user(subtype,type_id_client,id_client,email)
VALUES (register_subtype.subtype,register_subtype.type_id_client,register_subtype.id_client,register_subtype.email);
ELSE
UPDATE subtype_user sdu2 SET subtype=register_subtype.subtype,email=register_subtype.email
WHERE sdu2.id_client = register_subtype.id_client AND sdu2.type_id_client = register_subtype.type_id_client;
END IF;
END LOOP;
CLOSE cursor_subtype;
RETURN 'OK';
EXCEPTION WHEN OTHERS THEN
GET STACKED DIAGNOSTICS MESSAGE_EXCEPTION = MESSAGE_TEXT;
RETURN MESSAGE_EXCEPTION;
END; $$
LANGUAGE plpgsql;
It works, but When I run this function with the real table 1, it is not working. The function finishes but nothing happend. The real table 1 has 1 million of registers.

Answer 1

Row-by-row processing with embedded counting is a recipe for slow and inefficient processing. Additionally your check for existence won't work if the function is invoked from concurrent transactions. As far as I can tell you can replace the whole loop and cursor with a single INSERT statement:
CREATE OR REPLACE FUNCTION VERIFY_AND_INSERT_SUPTYPE()
RETURNS text
AS $$
DECLARE
MESSAGE_EXCEPTION TEXT;
BEGIN
INSERT INTO subtype_user(subtype, type_id_client, id_client, email)
SELECT tsd.subtype, tsd.type_id_client, tsd.id_client, tsd.email
FROM tmp_subtype tsd
ON conflict (id_client, type_id_client) DO UPDATE
SET subtype = excluded.register_subtype,
email = excluded.email;
RETURN 'OK';
EXCEPTION WHEN OTHERS THEN
GET STACKED DIAGNOSTICS MESSAGE_EXCEPTION = MESSAGE_TEXT;
RETURN MESSAGE_EXCEPTION;
END; $$
LANGUAGE plpgsql;
I probable would not add an exception handler to begin with, so that the caller sees the complete exception.

Answer 2

It is hard to say, what is wrong on this code - in this situation RAISE NOTICE is your best friend. I see some issues in your code, but these issues are related to performance. Table with 1 mil rows is nothing.
the code in ISAM programming style can be really slow - instead cycle over cursor use INSERT ON CONFLICT .. statement.
SELECT COUNT(*) ... can be rewritten to little bit faster, but surely more readable form:
IF EXISTS(SELECT ... FROM subtype_user) THEN
UPDATE ...
ELSE
INSERT ...
END IF;
Handling errors from your example is little bit obsolete - catch only exception that you can really solve. Your type of exception handling doesn't solve any, and more, you lose details info about the exception (position, line, ...). Just don't do it.