Auto-partitioning trigger doesn't work as expected - postgresql

Question

I'm trying to implement auto-partitioning of a table
CREATE TABLE incoming_ais_messages (
id uuid NOT NULL,
"source" int4 NOT NULL,
ais_channel varchar(8) NOT NULL,
is_read bool NOT NULL,
"time_stamp" timestamptz NOT null,
address_type varchar(32) NOT NULL,
"text" varchar NOT NULL,
CONSTRAINT incoming_ais_messages_pkey PRIMARY KEY (id,time_stamp)
) partition by range ("time_stamp");
For that I use a function:
create or replace function create_partition() returns trigger as $auto_partition$
begin
raise notice 'create_partion called';
execute 'create table if not exists incoming_ais_messages_partition_' || to_char(now()::date, 'yyyy_mm_dd') || ' partition of incoming_ais_messages
for values from (''' || to_char(now()::date, 'yyyy-mm-dd') || ''') to (''' || to_char((now() + interval '1 day')::date, 'yyyy-mm-dd') || ''');';
return new;
end;
$auto_partition$ language plpgsql;
And a trigger that should call it before any inserts:
create trigger auto_partition
before insert on incoming_ais_messages
for each row
execute procedure create_partition();
However when I insert something like:
INSERT INTO incoming_ais_messages (id, "source", ais_channel, is_read, "time_stamp", address_type, "text")
VALUES('123e4567-e89b-12d3-a456-426614174000'::uuid, 0, 'A', false, now(), 'DIRECT', 'text');
I get ther error:
SQL Error [23514]: ERROR: no partition of relation "incoming_ais_messages" found for row
Detail: Partition key of the failing row contains (time_stamp) = (2022-07-21 18:01:41.787604+03).
After that I created the partition manually:
create table if not exists incoming_ais_messages_partition_1970_01_01 partition of incoming_ais_messages
for values from (now()::date) to ((now() + interval '1 day')::date);
executed the same insert statement and got the error:
SQL Error [55006]: ERROR: cannot CREATE TABLE .. PARTITION OF "incoming_ais_messages" because it is being used by active queries in this session
Where: SQL statement "create table if not exists incoming_ais_messages_partition_2022_07_21 partition of incoming_ais_messages
for values from ('2022-07-21') to ('2022-07-22');"
PL/pgSQL function create_partition() line 4 at EXECUTE
Would be great to know what is wrong here. My solution is based on the approach described here https://evilmartians.com/chronicles/a-slice-of-life-table-partitioning-in-postgresql-databases
(Section: Bonus: how to create partitions)

Answer 1

PostgreSQL wants to know which partition the new rows will go into before it calls BEFORE ROW triggers, so the error is thrown before the CREATE gets a chance to run. (Note that the blog example is using a trigger on one table to create partition for a different table).
Doing what you want is possible (timescaledb extension does it, and you could research how if you want), but do yourself a favor and just pre-create a lot of partitions, and add a note to your calendar to add more in the future (as well as dropping old ones). Or write a cron job to do it.