Loop violating Primary Key Value - function

Question

I have a part of my function mentioned below.
When I execute the function I get an error saying primary key violation for alarm_id
SELECT COUNT(DISTINCT exception_sub_type) INTO v_count FROM mdas.alarm_configuration;
IF v_count > 0 THEN
FOR i IN 1..v_count
LOOP
SELECT ((MAX(alarm_id))+1) INTO v_alarm_id FROM mdas.alarm_configuration;
RAISE NOTICE 'ALARM ID (%)',v_alarm_id;
INSERT INTO mdas.alarm_configuration
(alarm_id,
exception_sub_type,
exception_type,
from_range,
groups,
priority,
sub_group,
to_range,
org_unit_id,
status)
SELECT DISTINCT ON(exception_sub_type) v_alarm_id,
exception_sub_type,
exception_type,
from_range,
v_group_name,
priority,
v_subgroup_name,
to_range,
v_org_unit_id,
status
FROM mdas.alarm_configuration
WHERE groups = v_group_name AND mdas.alarm_configuration.org_unit_id = v_org_unit_id;
END LOOP;
END IF;
Note: This is only a part of the function. The function has three arguments v_org_unit_id, v_group_name and v_subgroup_name. My primary key is on alarm_id, which I want to increment by 1 and insert based on the MAX which is available in the table.

Answer 1

In your environment, when more than two client call the function at the same time, they will see the same alarm_id, so raise unique violated.
for exp :
SESSION A :
select max(id) into v_id from test;
insert into test values (v_id);
.. not end else.
SESSION B :
select max(id) into v_id from test; -- this v_id will same as session a.
insert into test values (v_id);
and then session A commit;
SESSION B will raise error.
ERROR: duplicate key value violates unique constraint "test_pkey"
DETAIL: Key (id)=(?) already exists.
You can use PostgreSQL serial deal this problem.
LIKE :
digoal=# create table test (id serial primary key, other_cols type ...);
CREATE TABLE
and not need to use max(id), you only need type other columns's values.
like
insert into test (other_cols,...) values (...);