How to do a batch commit in plpgsql? - sql

Question

When I do the below function, some errors occurs:
**ddddl=# select sssss(1,10);
ERROR: cannot begin/end transactions in PL/pgSQL
HINT: Use a BEGIN block with an EXCEPTION clause instead.
CONTEXT: PL/pgSQL function sssss(integer,integer) line 8 at SQL statement**
Here is my sample code.
CREATE OR REPLACE FUNCTION sssss(
IN c_1 int,
IN f_i int
) returns void as
$$
DECLARE t_c INT;
BEGIN
t_c := f_i;
WHILE c_1 <= t_c
loop
IF MOD(c_1, 4) = 1 THEN
start transaction;
END IF;
-- My statements here.
IF MOD(c_1, 4) = 0 THEN
COMMIT;
END IF;
c_1 := c_1 + 1;
END loop;
COMMIT;
END;
$$ language plpgsql;
So could anyone give me a sample of how to finish my job as the above code?
I'm using PostgreSQL 9.2.

Answer 1

In general, I think there are three approaches you can take:
Do without. Just let the whole thing be committed at once, like PostgreSQL wants.
Write a wrapper in application code that sets up a transaction and calls your function. (This is simple to do in a shell script, for example.)
Use a hack. One hack that exists is, you can have your function create a database-link to your own database, and perform subtransactions via remote sessions. [More information.] (This is essentially equivalent to the "wrapper in application code" approach, except that the application code is still in PL/pgSQL.)

Answer 2

From Postgresql 12 onwards you can do batch commits if you use procedures instead of functions, invoked by CALL command. Therefore you're function will be rewritten like below and invoked with CALL command:
CREATE OR REPLACE PROCEDURE sssss(IN c_1 int,IN f_i int)
LANGUAGE plpgsql
AS $$
DECLARE
t_c INT;
BEGIN
t_c := f_i;
WHILE c_1 <= t_c
loop
-- My statements here.
IF MOD(c_1, 4) = 0 THEN
COMMIT;
END IF;
c_1 := c_1 + 1;
END loop;
COMMIT;
END;
$$;
CALL sssss(1,10);
More details about transaction management regarding Postgres are available here:
https://www.postgresql.org/docs/12/plpgsql-transactions.html