Partitioned tables cannot have ROW triggers. when adding a for each row trigger that calls a fn which creates a partition before inserting (postgres) - sql

Question

I am new to Database, so seeking some advise or help.
I have a table that is partitioned by list host, as shown below.
CREATE TABLE public. services
(
id integer,
service_name character varying(128),
host character varying(128),
) PARTITION BY LIST (host)
And to insert in the table, I have created a function that will check if the partitioned table is present if not, let's create one before inserting and trying to add a trigger to the function.
CREATE OR REPLACE FUNCTION service_function()
RETURNS TRIGGER AS $$
DECLARE
host TEXT;
partition_name TEXT;
BEGIN
partition_name := 'services_' || host;
IF NOT EXISTS
(SELECT 1
FROM information_schema.tables
WHERE table_name= partation_name)
THEN
RAISE NOTICE 'A partition has been created %', partition_name;
EXECUTE format(E'CREATE TABLE %I PARTITION OF services for values in (%L)'), partition_name, host;
END IF;
EXECUTE format('INSERT INTO %I (id, service_name, host) VALUES ($1, $2, $3)', partition_name) using NEW.id, NEW.service_name, NEW.host;
RETURN NULL;
Now when I am trying to add a trigger,
CREATE TRIGGER insert_service_trigger
BEFORE INSERT on services
FOR EACH ROW EXECUTE PROCEDURE service_function();
END
following error is thrown: ERROR: "services" is a partitioned table
DETAIL: Partitioned tables cannot have ROW triggers.
any suggestions or solution for it?
what I am trying to achieve: services table will be in 100G+ and always host will be there in where clause for all the SELECT queries, so I thought of creating a partition using host. is this is rite approach ??

Answer 1

You must be using PostgreSQL v10, which is the only release that ever sported that error message. Triggers on partitioned tables were introduced in v11.
But you won't be able to achieve what you want in any PostgreSQL version. By the time your trigger has started processing, it is too late too change the table definition. You'd get the following error:
ERROR: cannot CREATE TABLE .. PARTITION OF "services" because it is being used by active queries in this session
There is no way to achieve what you want in PostgreSQL. For a thorough discussion of this and possible workarounds, read my article.