CREATE OR REPLACE FUNCTION my_schema.big_function(my_arg character varying)
RETURNS text AS
$BODY$
BEGIN
    DROP TABLE IF EXISTS backend.table_B;
    CREATE TABLE backend.table_B AS
    --Create a table with a SELECT with some joins,
    --right now the resulting table is empty

    RAISE NOTICE 'table_B created';

    PERFORM my_schema.insert_from_shell(my_arg);

    RETURN 'Function Ended';
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;

CREATE OR REPLACE FUNCTION my_schema.insert_from_shell(my_arg character varying)
RETURNS text AS
$BODY$
#!/bin/sh
PGPASSWORD=mypassword psql -d mydatabase -h myhost -p myport -U myuser -c "INSERT INTO myschema.table_A(mycolumn) VALUES('$1')"
$BODY$
LANGUAGE plsh VOLATILE
COST 100;

SELECT my_schema.big_function('test');

SELECT my_schema.big_function('test');
SELECT my_schema.insert_from_shell('test');